This extension is Order Totals Module that allow you to charge a fixed or percentage fee for each payment. It is Multi Payment.

Demo:
http://www.webprojectsol.com/OpenCart/admin/
username: admin
password: admin
Extensions->Order Totals->Payment Type Charge->Edit

Features:
* Select one or many payments.
* Individual charge fee for each payment method.
* Fixed fee, percentage fee or both.
* Unlimited number of additional charge fee for each payment method.
* Set minimum amount for each payment method.
* Automatically applied to the cart total amount.