diff --git a/sale.py b/sale.py
index a2db878..213c657 100644
--- a/sale.py
+++ b/sale.py
@@ -14,9 +14,10 @@ class Sale(metaclass=PoolMeta):
 
     pizza_number = fields.Integer("Number pizza")
     total_discount = fields.Function(
-        Monetary("Total Discount", digits='currency', currency='currency'), 'get_amount')
-    total_discount_cache = Monetary(
-        "Total Discount cache", digits='currency', currency='currency')
+        Monetary(
+            "Total Discount", digits='currency', currency='currency'),
+        'get_amount')
+    total_discount_cache = fields.Numeric("Total Discount cache", digits='currency')
 
     @classmethod
     def __setup__(cls):
@@ -33,6 +34,25 @@ class Sale(metaclass=PoolMeta):
     def default_pizza_number(cls):
         return 0
 
+    @fields.depends('lines', 'currency', methods=['get_tax_amount'])
+    def on_change_lines(self):
+        self.untaxed_amount = Decimal('0.0')
+        self.tax_amount = Decimal('0.0')
+        self.total_amount = Decimal('0.0')
+        self.total_discount = Decimal('0.0')
+
+        if self.lines:
+            for line in self.lines:
+                self.untaxed_amount += getattr(line, 'amount', None) or 0
+            self.tax_amount = self.get_tax_amount()
+        if self.currency:
+            self.untaxed_amount = self.currency.round(self.untaxed_amount)
+            self.tax_amount = self.currency.round(self.tax_amount)
+        self.total_amount = self.untaxed_amount + self.tax_amount
+        if self.currency:
+            self.total_discount = self.currency.round(self.total_discount)
+            self.total_amount = self.currency.round(self.total_amount)
+
     @classmethod
     def store_cache(cls, sales):
         for sale in sales:
@@ -68,12 +88,12 @@ class Sale(metaclass=PoolMeta):
                     tax_amount[sale.id] = sale.tax_amount_cache
                     total_amount[sale.id] = sale.total_amount_cache
             else:
-                untaxed_amount[sale.id] = sum(
+                untaxed_amount[sale.id] = round(sum(
                     (line.amount for line in sale.lines
-                        if line.type == 'line'), Decimal(0))
-                total_discount[sale.id] = sum(
+                        if line.type == 'line'), Decimal(0)),2)
+                total_discount[sale.id] = round(sum(
                     (line.discount_amount for line in sale.lines
-                        if line.type == 'line'), Decimal(0))
+                        if line.type == 'line'), Decimal(0)), 2)
                 if compute_taxes:
                     tax_amount[sale.id] = sale.get_tax_amount()
                     total_amount[sale.id] = (