Online retail sales rose 15.6% last month, led largely by a jump in sales of luxury goods. Average transaction totals were slightly higher as well, according to MasterCard Advisors' SpendingPulse report. "The retailers who are growing are the ones who are growing e-commerce traffic," said industry research director Mike Berry. "Many of the drivers of the e-commerce space are pure e-commerce players. They don't even have a bricks-and-mortar presence."