The nation’s top court has opened the door for states to tax businesses outside their borders.That means an Illinois plan to expand online sales tax collection on certain businesses should also get the green light.State lawmakers approved the concept this spring, modeling the language on a South Dakota law under review by the U.S. Supreme Court.The plan imposes the state’s 6.25 percent use and service use taxes on retailers which may not be in Illinois, but which do either $100,000 or more in annual sales or …