The amount Americans tip on restaurant bills appears to be declining compared with five years ago, a new survey found.

The online poll of about 2,600 men and women in the U.S. found that a majority of Americans tip their food servers less than 20 percent and that one in 10 tip nothing at all.

Nearly 60 percent of those who said they tip less than 20 percent said the reason was that they "couldn't afford to on top of the cost of a meal," the survey reported.

Others -- about a third -- said they didn't tip 20 percent because they thought the service didn't merit a larger amount.

Respondents were also asked whether their tipping habits had changed in the past five years. Nearly half said they tip less now than in the past. The majority said the reason was that their financial situation had changed.

The survey was conducted by VoucherCloud.net, an online coupon website, as part of researching into consumers' spending habits.

It also found that generous tips were pretty rare: Only 23 percent of Americans tip their food servers 20 percent or more.