Russ, it is undoubtedly a hassle. Even before online sales. And even online.
Several Chicago suburbs span two counties, with different tax rates, of course. In my own suburb, I knew where the delineation is, so no problem. But for other art-fair venues, I had to search county boundaries online to determine which one applies. Then come mid-year tax-rate changes. Then art-fair organizes would advise you on one tax rate, but you'd discover that the online one is different.
It would be fair that, for online sales, only a single state sales tax applies, or even a single federal one.