round unit_price of invoice-line by price_digits

mixin.py

@@ -4,12 +4,13 @@
 # full copyright notices and license terms.
 
 
-from decimal import Decimal
+from decimal import Decimal, ROUND_HALF_EVEN
 import html
 from trytond.exceptions import UserError
 from trytond.i18n import gettext
 from trytond.tools import cached_property
 from trytond.pool import Pool
+from trytond.modules.product import price_digits
 
 
 class EdocumentMixin(object):
@@ -183,6 +184,21 @@ class EdocumentMixin(object):
                 taxname=tax.rec_name))
         return unece_category_code
 
+    def round_unitprice(self, value):
+        """ round value by digits in unit_price of account.invoice.line
+
+        Args:
+            value (Decimal): unit-price
+
+        Returns:
+            Decimal: rounded value
+        """
+        if isinstance(value, Decimal):
+            return value.quantize(
+                Decimal(str(1/10 ** price_digits[1])),
+                ROUND_HALF_EVEN)
+        return value
+
     def quote_text(self, text):
         """ replace critical chars
         """