I don't know the figures, but when a company reaches a certain dollar amount of sales in a state, they are required to start collecting sales tax.
Indiana has had a slot on the tax form for several years now to self report any purchases from out of state, online vendors so you can pay the sales tax they feel you owe...
I wouldn't say online doesn't have any advantages. At least with Target Sports, the Prime membership will help keep the cost below what you can usually find in a local store, even with tax added on. Plus the UPS guy drops my ammo off on my porch which reduces how far I have to carry cases of ammo...
Right, you're supposed to pay those taxes whether the online vendor collects the tax or not. Been that way a long time, over a decade at least.
... This "use tax" has been "required" for as long as I can remember.