"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.

Apparel, as usual, was mixed, posting a 2.1% increase. At 12% and 11%, respectively, were Ann Taylor and American Eagle Outfitters. However, Gap Inc. fell 6% and Cato Corp. dropped 2%, despite its 17% skyrocket in April.

Meanwhile, discount stores climbed 2.7%, lead by Target's 5.7% performance and Family Dollar's 4.5% rise. Wal-Mart reported a 2% increase.

ICSC's research team predicts that same-store sales this month will rise 3% due to a tough comparison to June last year, when same-store sales rose 5.2%.