Payment Doesn't Add Up Error Messge

[alinajenon]

Any thoughts on this one?  It has appeared on other time on a diff order, but I don't understand why.

Error Message    Transaction refused because of an invalid argument. See additional error messages for details.
Error Message    The totals of the cart item amounts do not match order amounts.

Joomla: 2.5.27
VM: 2.6.10

Thanks!
Alina

[alinajenon]

Replying once more to see if anyone might be able to offer me some more advice on how to adjust settings so that the cart calculations match the actual final total. (Right now it sometimes rounds the penny differently, so it ends up being 1 penny off and then the purchase doesn't go through).

Thanks much!
Alina