DAFpay fee rounding and an unchecked fee option

For GiveCampus payment setup.

The giving form displays the proposed optional transaction-fee contribution to the cent. When submitting through DAFpay, the server rounds that donor-covered amount upward to a whole dollar before adding it to the gift. For example, 61.03 becomes 62.00 in this path. The DAFpay prefill also sends a whole-dollar gift amount in cents to the provider. This explains the implementation's rounding; confirm the actual transaction before promising a correction or refund.

Covering the fee is optional in the form: an unchecked checkbox sets the additional fee to zero. You should not need to select an optional fee to enter your address. If the donor cannot proceed without it, treat that as a validation or checkout issue: collect the form, attempt time, browser, stage and exact visible error for support. Do not pay an optional fee just to bypass an error, and do not infer the fee percentage from one example.