diff --git a/purchase.py b/purchase.py
index e9ad0f14d8..1ffea9b8c7 100644
--- a/purchase.py
+++ b/purchase.py
@@ -189,12 +189,11 @@ class Purchase(OSV):
                 purchase, context=context))
             res.setdefault(purchase.id, Decimal('0.0'))
             for line in purchase.lines:
+                # Don't round on each line to handle rounding error
                 for tax in tax_obj.compute(
                     cursor, user, [t.id for t in line.taxes], line.unit_price,
                     line.quantity, context=ctx):
                     res[purchase.id] += tax['amount']
-                res[purchase.id] = currency_obj.round(cursor, user, purchase.currency,
-                        res[purchase.id])
             res[purchase.id] = currency_obj.round(cursor, user, purchase.currency,
                     res[purchase.id])
         return res