diff --git a/sale.py b/sale.py
index aacb941..3497c86 100644
--- a/sale.py
+++ b/sale.py
@@ -11,6 +11,9 @@ class Sale(metaclass=PoolMeta):
     __name__ = 'sale.sale'
 
     pizza_number = fields.Integer("Number pizza")
+    total_discount = fields.Function(Monetary("Total Discount", currency='currency', digits='currency'),
+                                    'get_amount')
+    total_discount_cache = Monetary("Total Discount cache", currency='currency', digits='currency')
 
     @classmethod
     def __setup__(cls):
@@ -27,6 +30,64 @@ class Sale(metaclass=PoolMeta):
     def default_pizza_number(cls):
         return 0
 
+    @classmethod
+    def store_cache(cls, sales):
+        for sale in sales:
+            sale.untaxed_amount_cache = sale.untaxed_amount
+            sale.tax_amount_cache = sale.tax_amount
+            sale.total_amount_cache = sale.total_amount
+            sale.total_discount_cache = sale.total_discount
+        cls.save(sales)    
+    
+    @classmethod
+    def get_amount(cls, sales, names):
+        untaxed_amount = {}
+        tax_amount = {}
+        total_amount = {}
+        total_discount = {}
+        if {'tax_amount', 'total_amount'} & set(names):
+            compute_taxes = True
+        else:
+            compute_taxes = False
+        # Sort cached first and re-instanciate to optimize cache management
+        sales = sorted(sales, key=lambda s: s.state in cls._states_cached,
+            reverse=True)
+        sales = cls.browse(sales)
+        for sale in sales:
+            if (sale.state in cls._states_cached
+                    and sale.untaxed_amount_cache is not None
+                    and sale.tax_amount_cache is not None
+                    and sale.total_amount_cache is not None
+                    and sale.total_discount is not None):
+                untaxed_amount[sale.id] = sale.untaxed_amount_cache
+                total_discount[sale.id] = sale.total_discount_cache
+                if compute_taxes:
+                    tax_amount[sale.id] = sale.tax_amount_cache
+                    total_amount[sale.id] = sale.total_amount_cache
+            else:
+                untaxed_amount[sale.id] = sum(
+                    (line.amount for line in sale.lines
+                        if line.type == 'line'), Decimal(0))
+                total_discount[sale.id] = sum(
+                    (line.discount_amount for line in sale.lines
+                        if line.type == 'line'), Decimal(0))              
+                if compute_taxes:
+                    tax_amount[sale.id] = sale.get_tax_amount()
+                    total_amount[sale.id] = (
+                        untaxed_amount[sale.id] + tax_amount[sale.id])
+
+        result = {
+            'untaxed_amount': untaxed_amount,
+            'tax_amount': tax_amount,
+            'total_amount': total_amount,
+            'total_discount': total_discount,
+            }
+        for key in list(result.keys()):
+            if key not in names:
+                del result[key]
+
+        return result
+
     def get_invoice_resolution(subtype):
         if subtype:
             resolution = subtype.sequence.invoice_resolution
diff --git a/view/sale_form.xml b/view/sale_form.xml
index e29bdd4..dff9d0b 100644
--- a/view/sale_form.xml
+++ b/view/sale_form.xml
@@ -12,4 +12,8 @@ this repository contains the full copyright notices and license terms. -->
 	</group>
 	<newline/>
     </xpath>
+    <xpath expr="/form/notebook/page[@id='purchase']/group[@id='amount']/field[@name='tax_amount']" position="after">
+		<label name="total_discount"/>
+		<field name="total_discount"/>
+    </xpath>
 </data>