Retailers placed orders well in advance of October and U.S. Customs and Border Protection inspectors were kept on the job, while other federal workers were furloughed, the NRF said.
"Cargo arriving at the ports in October and for most of the rest of the year was ordered long before anyone ever heard of a shutdown," said NRF vice president for supply chain and customs policy Jonathan Gold.
"The question at this point isn't how much merchandise arrived but how much consumers bought and how they are going to react as economic talks continue in Washington," Gold said in a statement.
The trade group predicted in early October that this year's holiday sales would grow 3.9 percent over the same period of 2012, climbing to a total of $602.1 billion.
Part of that estimate is based on the volume of retail containers coming into U.S. ports.
NRF said the bulk of imported holiday sales items arrive in August, September and October. This year, 4.35 million cargo containers were handled at U.S. ports in those three months, which is a 4.3 percent increase over August through October in 2012.
Import figures were provided by the monthly Global Port Tracker report released by the NRF and Hackett Associates, the trade group said.