Many online payment gateways already offer some kind of sales tax API. Keep in mind in California, sales tax changes per county. In places like Tennessee, the tax rate can change if your item is a grocery or isn't a grocery.
There are companies that already sell massive lookup tables or API access to calculate a lot of this stuff. I think for most retailers, this won't be that big a change.
Most mom-and-pop online stores have disappeared too. Gone are the days when you went to Pricewatch.com and Pricescan.com. Now all the individual shops just create a store on Newegg, Amazon and eBay. I'm pretty sure the big players will start offering up tools to do these calculations for them as well.
There are companies that already sell massive lookup tables or API access to calculate a lot of this stuff. I think for most retailers, this won't be that big a change.
Most mom-and-pop online stores have disappeared too. Gone are the days when you went to Pricewatch.com and Pricescan.com. Now all the individual shops just create a store on Newegg, Amazon and eBay. I'm pretty sure the big players will start offering up tools to do these calculations for them as well.