Round Dominican invoice taxes independently

__init__.py

@@ -1,6 +1,6 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
 
-from . import tax
+from . import invoice, tax
 
-__all__ = ['tax']
+__all__ = ['invoice', 'tax']

invoice.py

@@ -0,0 +1,39 @@
+"""Dominican invoice tax rounding policy.
+
+Tryton's generic taxable mixin compensates the aggregate currency-rounding
+remainder on the first non-zero tax.  That keeps the rounded aggregate equal
+to the aggregate of the unrounded taxes, but it can change the reported value
+of a specific Dominican tax (ITBIS, ISC or CDT).
+
+Dominican fiscal documents state every tax in currency precision.  Each tax
+must therefore retain its own rounded result; no residual is redistributed
+between different tax liabilities or tax credits.
+"""
+
+from trytond.model import fields
+from trytond.pool import PoolMeta
+
+
+def round_taxes_independently(currency, taxes):
+    """Round every tax amount without reallocating the aggregate residual."""
+    if not currency:
+        return
+    for taxline in taxes.values():
+        taxline.amount = currency.round(taxline.amount)
+
+
+class IndependentTaxRoundingMixin:
+
+    __slots__ = ()
+
+    @fields.depends('currency')
+    def _round_taxes(self, taxes):
+        round_taxes_independently(self.currency, taxes)
+
+
+class Invoice(IndependentTaxRoundingMixin, metaclass=PoolMeta):
+    __name__ = 'account.invoice'
+
+
+class InvoiceLine(IndependentTaxRoundingMixin, metaclass=PoolMeta):
+    __name__ = 'account.invoice.line'

tests/test_module.py

@@ -4,12 +4,15 @@ from collections import Counter
 from configparser import ConfigParser
 from decimal import Decimal
 from pathlib import Path
+from types import SimpleNamespace
 from xml.etree import ElementTree as ET
 
 from trytond.pool import Pool
 from trytond.tests.test_tryton import ModuleTestCase, with_transaction
 from trytond.transaction import Transaction
 
+from trytond.modules.account_do.invoice import round_taxes_independently
+
 MODULE_DIR = Path(__file__).resolve().parent.parent
 
 TAX_CODE_LINE_AUDIT = {
@@ -125,6 +128,56 @@ class AccountDoTestCase(ModuleTestCase):
         'account_stock_continental',
         ]
 
+    @with_transaction()
+    def test_invoice_taxes_round_independently(self):
+        """A rounding residual must not change ITBIS, ISC or CDT."""
+        pool = Pool()
+        Currency = pool.get('currency.currency')
+        currency, = Currency.create([{
+                    'name': 'Peso dominicano',
+                    'code': 'DOP',
+                    'symbol': 'RD$',
+                    'digits': 2,
+                    'rounding': Decimal('0.01'),
+                    }])
+        taxes = {
+            'itbis': SimpleNamespace(amount=Decimal('91.8036')),
+            'isc': SimpleNamespace(amount=Decimal('51.0020')),
+            'cdt': SimpleNamespace(amount=Decimal('9.9000')),
+            }
+
+        round_taxes_independently(currency, taxes)
+
+        self.assertEqual(taxes['itbis'].amount, Decimal('91.80'))
+        self.assertEqual(taxes['isc'].amount, Decimal('51.00'))
+        self.assertEqual(taxes['cdt'].amount, Decimal('9.90'))
+        self.assertEqual(
+            sum(tax.amount for tax in taxes.values()), Decimal('152.70'))
+
+    @with_transaction()
+    def test_invoice_credit_note_taxes_round_independently(self):
+        """The same policy applies symmetrically to credit notes."""
+        pool = Pool()
+        Currency = pool.get('currency.currency')
+        currency, = Currency.create([{
+                    'name': 'Peso dominicano',
+                    'code': 'DOP',
+                    'symbol': 'RD$',
+                    'digits': 2,
+                    'rounding': Decimal('0.01'),
+                    }])
+        taxes = {
+            'itbis': SimpleNamespace(amount=Decimal('-91.8036')),
+            'isc': SimpleNamespace(amount=Decimal('-51.0020')),
+            'cdt': SimpleNamespace(amount=Decimal('-9.9000')),
+            }
+
+        round_taxes_independently(currency, taxes)
+
+        self.assertEqual(taxes['itbis'].amount, Decimal('-91.80'))
+        self.assertEqual(taxes['isc'].amount, Decimal('-51.00'))
+        self.assertEqual(taxes['cdt'].amount, Decimal('-9.90'))
+
     @with_transaction()
     def test_chart_template_is_loaded_by_default(self):
         'Test English Dominican chart is loaded in an English database'
@@ -571,7 +624,7 @@ class AccountDoUnitTestCase(unittest.TestCase):
         self.assertEqual(config.get('tryton', 'version'), '8.0.5')
         self.assertEqual(
             set(lines('tryton', 'depends')),
-            {'account', 'ir'})
+            {'account', 'account_invoice', 'ir'})
         self.assertEqual(
             lines('tryton', 'xml'),
             [
@@ -587,7 +640,13 @@ class AccountDoUnitTestCase(unittest.TestCase):
                 ])
         self.assertEqual(
             lines('register', 'model'),
-            ['ir.ModelData', 'tax.TaxTemplate', 'tax.Tax'])
+            [
+                'ir.ModelData',
+                'invoice.Invoice',
+                'invoice.InvoiceLine',
+                'tax.TaxTemplate',
+                'tax.Tax',
+                ])
         self.assertEqual(lines('register', 'wizard'), ['account.CreateChart'])
         for filename in lines('tryton', 'xml'):
             self.assertTrue((MODULE_DIR / filename).is_file())

tryton.cfg

@@ -2,6 +2,7 @@
 version=8.0.5
 depends:
     account
+    account_invoice
     ir
 xml:
     account_chart_do_en.xml
@@ -17,6 +18,8 @@ xml:
 [register]
 model:
     ir.ModelData
+    invoice.Invoice
+    invoice.InvoiceLine
     tax.TaxTemplate
     tax.Tax
 wizard: