Add round_price

We add a common method to round prices that are stored using the price digits.
It is useless to use the digits from the field because it can not be changed in
any other way than by configuration.

issue9146
review299521002

account.py

@@ -1,12 +1,10 @@
 # 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 decimal import Decimal
-
 from trytond.model import fields
 from trytond.pool import PoolMeta, Pool
 from trytond.pyson import Eval
 
-from trytond.modules.product import price_digits
+from trytond.modules.product import price_digits, round_price
 
 
 class InvoiceLine(metaclass=PoolMeta):
@@ -86,10 +84,11 @@ class InvoiceLine(metaclass=PoolMeta):
         Uom = pool.get('product.uom')
         if (self.unit_price is not None and self.unit and self.secondary_unit
                 and (self.secondary_uom_factor or self.secondary_uom_rate)):
-            return Uom.compute_price(
+            unit_price = Uom.compute_price(
                 self.unit, self.unit_price, self.secondary_unit,
                 factor=self.secondary_uom_factor, rate=self.secondary_uom_rate
-                ).quantize(Decimal(1) / 10 ** price_digits[1])
+                )
+            return round_price(unit_price)
         else:
             return None
 
@@ -104,7 +103,8 @@ class InvoiceLine(metaclass=PoolMeta):
             self.unit_price = Uom.compute_price(
                 self.secondary_unit, self.secondary_unit_price, self.unit,
                 factor=self.secondary_uom_rate, rate=self.secondary_uom_factor
-                ).quantize(Decimal(1) / 10 ** price_digits[1])
+                )
+            self.unit_price = round_price(self.unit_price)
             self.amount = self.on_change_with_amount()
 
     @fields.depends(methods=[