If I could wave a wand and go back 40 years, I would be charging a flat rate for my payroll software, and a separate fee by state, for the states with WH. (See the thread on the upcoming AL change. I will likely be spending many hours on a small percentage of customers this fall.)
I may actually implement something along this in a few years, keeping the fee the same for the no hassle (no state WH states) and only the next increase for the rest of the states. Have to balance it though, as more prices means more complication, and zero chance of automated orders, so never mind .