Within your Company Setup you can set fees/surcharges to be automatically applied when Customers pay via credit card.

Navigate to Company Admin > Company Setup > Finance

Here you can enter values for:

Customer Credit Card Fee (Paid by Customer to Agent for payments via Agent Merchant Facility) is the value that you will charge customers when they pay via your credit card facility. The figure will be automatically added to the Quote so you can advise customers to complete amount due.

Hero Payments Fee (Paid by Customer to Agent for payments via Hero Payments)

is the value you charge customers when they pay via Hero's merchant facility. For more information on this, click here.