Round Dominican invoice taxes independently

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'