My client would like to add a checkbox on the checkout page that would allow the user to add a set donation amount to there order. For example, user is reg. for a seminar, which cost $100, upon checkout in the custom fields, there would be a box that says something like, "Yes, I would like to donate $50 to something, something..., etc.". Once the box is checked, it would add the $50 to the total.
Is this possible?