Ankeny-based Casey’s General Store was among a dozen companies nationwide to receive letters from the U.S. Food and Drug Administration calling out what the agency called a “violative history” of illegal tobacco sales to minors.In the letters, dated April 5, then-FDA Commissioner Scott Gottlieb asked the chains to write back within 30 days with a “detailed plan” and time frames for reducing the sales to minors.“Violating the law preventing sales of tobacco products to minors, and paying associated fines and penalties, should not simply be viewed as a cost of doing business,” Gottlieb wrote.