This decision enables a state-imposed tax on inter-state shipping of goods purchased in other states (via mail-order catalogues or internet e-commerce -- aka "virtual showrooms" as Kennedy's decision calls a website, in order to drop the now-abandoned requirement for "physical presence").

Don't be fooled by it being labeled a "sales tax". In actual fact, the Supreme Court has enabled tariffs between the US States. Which is exactly what the Commerce Clause was intended to prevent.