Round only the tax amount of the line when rounding per line

If we round the tax amount already added to the other line, the result may vary
depending on the order of the lines.
This is because round half even is used so the result may depend on the already
summed tax amounts.

Closes #14047
(grafted from e1e376f91bc1e111cdef39ddcbbfd92d201ea6c9)

--HG--
branch : 7.0

modules/account/tax.py

@@ -1307,14 +1307,20 @@ class TaxableMixin(object):
                         if self.currency:
                             taxline['base'] = self.currency.round(
                                 taxline['base'])
-                        if taxline not in taxes:
-                            taxes[taxline] = taxline
+                        if taxline not in current_taxes:
+                            current_taxes[taxline] = taxline
                         else:
-                            taxes[taxline]['base'] += taxline['base']
-                            taxes[taxline]['amount'] += taxline['amount']
-                        current_taxes[taxline] = taxes[taxline]
+                            current_taxes[taxline]['base'] += taxline['base']
+                            current_taxes[taxline]['amount'] += (
+                                taxline['amount'])
                     if tax_rounding == 'line':
                         self._round_taxes(current_taxes)
+                    for key, taxline in current_taxes.items():
+                        if key not in taxes:
+                            taxes[key] = taxline
+                        else:
+                            taxes[key]['base'] += taxline['base']
+                            taxes[key]['amount'] += taxline['amount']
                 if tax_rounding == 'document':
                     self._round_taxes(taxes)
                 for key, taxline in taxes.items():

modules/account/tests/test_module.py

@@ -1143,6 +1143,38 @@ class AccountTestCase(
         self.assertEqual(tax['base'], Decimal('100.00'))
         self.assertEqual(tax['amount'], Decimal('20.00'))
 
+    @with_transaction()
+    def test_taxable_mixin_line2(self):
+        "Test TaxableMixin with rounding on line"
+        pool = Pool()
+        Tax = pool.get('account.tax')
+        Configuration = pool.get('account.configuration')
+        currency = create_currency('cur')
+
+        company = create_company()
+        with set_company(company):
+            create_chart(company, tax=True)
+            tax, = Tax.search([])
+            tax.rate = 1
+            tax.save()
+            config = Configuration(1)
+            config.tax_rounding = 'line'
+            config.save()
+
+            taxable = self.Taxable(
+                currency=currency,
+                taxable_lines=[
+                    ([tax], Decimal('1.070'), 1, None),
+                    ([tax], Decimal('1.005'), 1, None),
+                    ],
+                company=company)
+
+            taxes = taxable._get_taxes()
+
+        tax, = taxes
+        self.assertEqual(tax['base'], Decimal('2.07'))
+        self.assertEqual(tax['amount'], Decimal('2.07'))
+
     @with_transaction()
     def test_taxable_mixin_document(self):
         "Test TaxableMixin with rounding on document"