The National Association of Realtors reported that existing home sales dipped 2.2% last month to a seasonally adjusted annual rate of 5.66 million units, down from the upwardly revised rate of 5.79 million in April. Sales year-over-year were up 19.2%.

Analysts surveyed by Briefing.com were looking for resales in May to rise to an annual rate of 6.1 million units.

Although homebuyers had to sign contracts by the end of April to qualify for a tax credit up to $8,000, they have until the end of June to close deals. Existing home sales data is based on transaction closings, so figures still reflect strong interest in the credit.

So the tax credit, stabilizing home prices and low mortgage rates kept sales at elevated levels last month, said Lawrence Yun, NAR chief economist.

"We are witnessing the ongoing effects of the homebuyer tax credit, which we'll also see in June real estate closings," Yun said.

The Senate could pass an amendment to push the closing deadline back to Sept. 30 as part of a controversial job and tax bill.

Price and inventory: The NAR report showed that the median price of homes sold in May was $179,600, up 2.7% from a year ago. Just under a third of homes sold during the month were distressed properties.

Total housing inventory fell 3.4% to 3.89 million existing homes for sale. That represents a 8.3-month supply at the current sales pace, down from a 8.4-month supply in April. A six month of supply is considered normal.

Sales by property and region: Sales of single-family homes declined 1.6% in May compared to the prior month, while condominium and co-op sales sank nearly 7%.