eCommerce/shopping site & local sales taxes

[fishtech]

We are looking to publish a simple shopping cart system using FMSA and php.

One thing I cannot find addressed anywhere is how local US sales taxes should be applied to orders.

My company has presence in 15 states, and we need to charge different levels of sales tax to purchasers from those states. In addition the sales tax can vary from county-to-county within each state.

I know when I purchase something from apple.com I am specifically asked which county I live in for this very reason.

I found http://ws.cdyne.com/NatTax/taxquery.asmx?op=GetTaxInformation which offers an api for this service. But I am wondering if this is the best way to go?

So has anyone been here & done this?

Thanks,

ft.