Here is the breakdown of how Rerun calculates discounts, surcharges, and taxes on a payment stream or one-time payment:

Rerun allows you to add credit card surcharges now to your Rerun payments, however, there are some rules and regulations that you must follow within the U.S. If you add a surcharge to a payment, you are responsible as the merchant to adhere to any laws/regulations surrounding surcharges.

What is a Surcharge?

A credit card surcharge is a fee that a retailer adds to the cost of a purchase when a customer uses a credit card. Surcharging isn’t allowed everywhere. Currently, there are laws limiting surcharging in: California, Colorado, Connecticut, Florida, Kansas, Maine, Massachusetts, Oklahoma, Texas and Utah.

Read more at: https://usa.visa.com/dam/VCOM/download/merchants/surcharging-faq-by-merchants.pdf