As tax day approaches (the death march that comes for us all), yoga studios throughout the five boroughs are increasingly being audited by the state. That’s because, until last summer, most thought they were exempt from the city’s 4.5 percent sales tax. They have since been classified as weight-control or health-salon businesses, a decision that could cost some studios as much as $100,000, depending on their size, and include back taxes for the last three years. Which means the city’s legions of mat-toting, Lululemon-sporting yoga afficionados may soon be paying more for their zen. [WSJ]