Florida state rate (6%), the county rate (0% to 2%). There is no city sale tax for the Florida cities.
Source:
http://www.salestaxstates.com/sales-tax-calculator-florida
There are 45 states plus the District of Columbia that impose a state sales tax on retirees and other residents. In addition, local sales tax is collected in 38 states. The combined levy can be hefty. In Tennessee, for example, the average combined state and local sales tax is 9.46%.
Alaska, Delaware, Montana, New Hampshire and Oregon. Do not charge a sales tax, however Alaska allows municipalities to charge local sales taxes.
Source:
https://www.kiplinger.com/slideshow/retirement/T055-S001-5-states-with-no-state-sales-tax/index.html
If you Ban certain states based on the sales tax, you are banning 45 out of 50 states from buying your domains. That's a large chunk of the USA that you are losing.
Again, we have the issue of: What is considered an online retailer? It is important to note that "Online Retailer" is going to be defined by the law that is in effect at the Buyers location, not the sellers.
Like you said, SCOTUS has ruled to allow the collection of sales tax, but, I am going to step out of a limb and assume that most of the 45 states collecting sales taxes will require that online retailers collect it. I assume this since it was the states that have made the push to the Supreme Court.
So far the calculator cited above is the best tool I have found to work with the potential new regulation. Just keep in mind that regardless of what platform you sell on, it is the law in effect at the buyers location that is going to be the law that governs what actions you must take.
Regardless of the platform you choose to sell on:
Ultimately, it is the responsibility of the seller to make sure that they are in compliance with all laws, much like it is the responsibility of the buyer to perform their due diligence.
I hope it is an easy transition, but with the many tax zones that the USA has and with that many changing tax laws, I feel like it is going to end up being more confusing than it has to be.