I don’t pay sales tax when I order from Amazon or Adorama and I’m already a prime member of Amazon but that works for me as I mostly buy online.
For Amazon the issue of sales tax depends on a number of things starting with the state you live in and the State & local sales tax rates there. Also if Amazon has a physical presence in your state they are obliged to charge all State and local taxes. So I can only assume that Amazon does not have a physical presence in your state.
I live in California, and even with Amazon Prime I am charged sales tax on most of the purchases I make through them. My large ticket photography hardware, and other stuff, I buy from B&H, and Adorama online for now neither of those stores charge me for my online purchases, and they always pick up 48 State shipping charges.
I have a feeling those days of B&H, and Adorama purchases free of State tax charges are numbered.