MvCool - The Miva Merchant Module Superstore Addendum Checkout Questions Slide 4
Setting up the fee in admin (compiled version)
Setting up the fee in admin (compiled version)
You can easily setup the fee in admin. In the example shown here you can see that I have applied a negative $1 as an incentive called Dollar Days Discount. The fee is activated if the customer responds to the checkbox which has a value of Yes. If they don't check the box, there is no value and thus, no fee. There is also the option of making the fee taxable, as specified in the far right column in this configuration.

Also pictured here is the optional labels you can prefix each response with in the emails, batch, and invoice.