Polls are closing in Vermont, Virginia, and Georgia, three of the 10 Super Tuesday states, but voting is continuing in seven other contests, including Massachusetts, on a night that could change the shape of the race for the GOP presidential nomination. The latest high-stakes round in the grueling, sometimes nasty, battle for the Republican nod could determine whether former Massachusetts governor Mitt Romney solidifies his frontrunner status or faces bitterly contested primaries for weeks to come. The most-watched contests are in Ohio, where Romney was statistically tied in polls with Rick Santorum, and in Tennessee, where Newt Gingrich’s late-breaking strength could be a major factor. Altogether, as many as 437 delegates are at stake in the 10 races.