Respondents argue that “the physical presence rule has permitted start-ups and small businesses to use the Internet as a means to grow their companies and access a national market, without exposing them to the daunting complexity and business-development obstacles of nationwide sales tax collection.” These burdens may pose legitimate concerns in some instances, particularly for small businesses that make a small volume of sales to customers in many States. State taxes differ, not only in the rate imposed but also in the categories of goods that are taxed and, sometimes, the relevant date of purchase. Eventually, software that is available at a reasonable cost may make it easier for small businesses to cope with these problems. Indeed, as the physical presence rule no longer controls, those systems may well become available in a short period of time, either from private providers or from state taxing agencies themselves. And in all events, Congress may legislate to address these problems if it deems it necessary and fit to do so.
In this case, however, South Dakota affords small merchants a reasonable degree of protection. The law at issue requires a merchant to collect the tax only if it does a considerable amount of business in the State; the law is not retroactive; and South Dakota is a party to the Streamlined Sales and Use Tax Agreement, see infra at 23.