We know as well as every merchant, giving prime parking space and dedicating it to customers with disabilities is mandatory.
While not as convenient for walking customers, we actually see many customers with disabilities use regular designated customer parking. (aside the parking cheaters).
Think of your checkout lanes and sales and service counters in the same way. In other words, there has to be designated checkout lanes and sales and service counters specifically as accessibility checkouts.
The importance here is that your checkout is far more valuable to the bottom line than the designated accessible parking is. It is the most frequented customer space in a place of business. Fully accessible now makes total sense.
The ADA.Gov and U.S. Access Board requires one lane of every four lanes must be designated accessible and each individual checkout sales and services counter (example in-store pharmacy or returns).