U.S. retailers are extending deals into Cyber Monday and beyond to try to sustain a 13 percent gain in Thanksgiving weekend sales.

"Year over year, Black Friday sales were strong and margins should have also been strong," said a Bloomberg Industries analyst.

The National Retail Federation said yesterday it predicts holiday sales, including online, will rise 4.1 percent to about $586.1 billion this year, compared with a 5.6 percent gain in 2011. (READ the Bloomberg story in Business Week)