GOODLETTSVILLE, Tenn.--(BUSINESS WIRE)--Dollar General Corporation (NYSE: DG) today reported financial results for its fiscal 2015 second quarter (13 weeks) ended July 31, 2015. “Dollar General achieved strong financial performance in the second quarter. We delivered 7.9 percent sales growth, 2.8 percent same-store sales growth, robust gross margin expansion and 14 percent diluted EPS improvement over the 2014 second quarter. We also grew both customer traffic and average ticket for the 30th co