Well as a small business owner. You need to look at the south dakota vs wayfair inc case. Where the supreme court ruled where states can require sales tax from out of state purchases.
For example:
If my business was located in Indiana and I will selling to a Michigan customer I would not have to charge sales tax unless the year prior I made 200 sales or a 100,000 dollars in sales to Michigan Residents. I used michigan as an example because thats the state I live and the state im most familar with.
Forget the above example now because I am actually based in michigan.
New example:
Moored performance is located in michigan. Even if I only ever make 1 sale online I am still required to collect sales tax to michigan residents since my busniess is based here. This is only for products sold not a service. So I do not have to charge taxes on my tunes. Well I shouldnt the state of michigan wants to have more conversations with me on exactly what I am doing because they dont understand. I pretty much told them remote tune ups. And they just cant get over the fact software is involved.
But the interesting thing. from what I can tell the State of Tennessee never requires a seller from another state to charge a Tennessee resident. My guess some places are just starting to always charge sales tax because they don't want to know every states tax code.