@cmaddox issue you would run into is compliance and ease.  You would need to add it and remove it if the customer chooses to do debit or echeck/check payment.  I suppose if you know in advance that a customer is paying CC then ad hoc you can add it and that solves the expense.  But in my expierence if you do any sort of volume in invoices or transactions this process can get time intensive very quickly.

Happy to share a solution we implement for clients which does this automatically and adds the cc fee automatically when customers choose to pay via cc.

Aaron