diff --git a/addons/point_of_sale/point_of_sale.py b/addons/point_of_sale/point_of_sale.py
index ff662645a62..aac025f38d6 100644
--- a/addons/point_of_sale/point_of_sale.py
+++ b/addons/point_of_sale/point_of_sale.py
@@ -1044,7 +1044,7 @@ class pos_order(osv.osv):
                 tax_amount = line.price_subtotal * tax['base_sign']
             else:
                 tax_code_id = tax['ref_base_code_id']
-                tax_amount = line.price_subtotal * tax['ref_base_sign']
+                tax_amount = -line.price_subtotal * tax['ref_base_sign']
 
             return (tax_code_id, tax_amount,)
 
@@ -1140,7 +1140,10 @@ class pos_order(osv.osv):
 
                 for tax in computed_taxes:
                     tax_amount += cur_obj.round(cr, uid, cur, tax['amount'])
-                    group_key = (tax['tax_code_id'], tax['base_code_id'], tax['account_collected_id'], tax['id'])
+                    if tax_amount < 0:
+                        group_key = (tax['ref_tax_code_id'], tax['base_code_id'], tax['account_collected_id'], tax['id'])
+                    else:
+                        group_key = (tax['tax_code_id'], tax['base_code_id'], tax['account_collected_id'], tax['id'])
 
                     group_tax.setdefault(group_key, 0)
                     group_tax[group_key] += cur_obj.round(cr, uid, cur, tax['amount'])
@@ -1213,7 +1216,7 @@ class pos_order(osv.osv):
                     'credit': ((tax_amount>0) and tax_amount) or 0.0,
                     'debit': ((tax_amount<0) and -tax_amount) or 0.0,
                     'tax_code_id': key[tax_code_pos],
-                    'tax_amount': tax_amount,
+                    'tax_amount': abs(tax_amount),
                     'partner_id': order.partner_id and self.pool.get("res.partner")._find_accounting_partner(order.partner_id).id or False
                 })