All online merchants like Walmart, Kohls, Penneys, charge sales tax. Aliexpress and Ebay also charge me tax now, although I wonder if my state (Illinois) actually sees it. I think Amazon is catching up, now forcing a sales tax on their associate sellers.
I see that RAD charges sales tax. I would expect all the bigger sellers have the mechanism in place. They probably use a web template that figures shipping and sales tax.