(a) If a county tax assessor-collector accepts a credit card invoice as conditional payment of a fee or tax, the assessor-collector may collect a fee for processing the invoice.
(b) The assessor-collector shall set a fee collected under Subsection (a) in an amount that is reasonably related to the expense incurred in processing the credit card invoice, not to exceed five percent of the amount of the fee or tax. The processing fee is in addition to the amount of the fee or tax, and may be paid conditionally by including the amount of the processing fee on the credit card invoice.