"Even with all the concerns over higher energy costs throughout the month, there remains an underlining breath of strength within consumer spending and the non-automotive retail spending categories," says Michael Niemira, ICSC's chief economist and director of research.

Department stores were the biggest surprise for the month, rising 6.7% as a group. J.C. Penney came in the highest, with a 11.1% boost, followed by Federated Department Stores, up 9.2% and bouncing back from a rough April when the chain's sales fell 0.8%. At the low end of the spectrum was Saks Inc., which inched up 1.1%.

Wholesale clubs were the best-performing chains, gaining 7.2%. Costco Wholesale jumped 10%, followed by a 4.2% lift by BJ's Wholesale and a 4% push at Wal-Mart's Sam's Clubs.