[rascul]

> a reverse IP lookup should give you a good estimate

Not really, no.

[perfectstorm]

care to elaborate on that? also, it's not that hard to ask users to enter their shipping zip code to get more accurate prices. some websites do that already nowadays. my point is reverse ip lookup is a good enough starting point for the first estimation.

[rascul]

IP addresses aren't related to locations. A third party database with voluntary contributions isn't exactly reliable and is frequently incorrect.

Zip codes also aren't great either. A single zip code can cover many different tax jurisdictions, even different states.