> Checking against a particular table to see the sales tax rate and then calculating it and adding it to a particular line item wouldn't be all that complicated.
Each state has a table. You have to look up the zip code to cross to a county to see what the county's tax rate is because some county's add 0.5 to 1% above the state's. Some cities have a tax, too, so this has to be taken into account. These tables change all the time. Then you have some goods that are taxable and some that are not. Florida, for example, does not tax foods. Then you also have "tax free" periods like back to school. Which state is doing that which weekend or week? Its a huge mess for any small company to deal with. Only the big companies can navigate this.
It would be a wise business strategy for the incumbents to back this idea/bill as a way of sealing off any new comers.