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Kai Ryssdal: Tell me if this has happened to you recently at the supermarket. You unload your basket onto the conveyor belt, browse the tabloids as you wait for the cashier, and then that cashier hits you up for a donation while he's ringing up your groceries. It's tough to get through your shopping these days without being asked to give to one thing or another. A dollar here and a dollar there can really add up for what are often worthy causes. But Michael May explains that there are some hidden costs.

DAVID FICKECK: Would you like to make a donation to the KEYE food drive today? They're a $1, $5 donation, or you can pick a bag over here we can gladly scan for you.

That's David Fickeck, a cashier and store director at the Randall's supermarket in Austin, Texas. He does more than ring up groceries. He's a fundraiser.

Randall's supermarket is owned by Safeway, which does four national charity drives each year in its more than 1500 stores. The regional chains, like Randall's, can elect to do other drives as well, like this one benefiting the food bank. Connie Yates is director of public affairs for Randall's.

CONNIE Yates: It's very important to give back to the community. It's very important to be involved in charities that matter to our customers.

The drive raises $15,000, and about 10,000 pounds of food. Kerri Qunell is with the Capital Area Food Bank. She says Randall's was the first supermarket to do a checkout charity drive in Austin.

KERRI Qunell: Since then there have been other programs that have blossomed in our community and across the country to replicate that. So it is becoming a more popular and more convenient way for grocery shoppers to be able to donate to their local food bank.

And all sorts of other charities. That can put pressure on workers, who have to do the asking. Ron Lind is the president of UFCW local 5, a union that represents supermarket employees. He told me that workers have complained about being pressured to solicit. And when I asked some Randall's shoppers what they thought of the checkout charity drive, they were divided.

Emily Hampton gives at the register, but doesn't like being confronted every time she shops.

EMILY HAMPTON: Yeah, it does really put you on the spot. And when you say no, the people around you, at the back of the line, I'm thinking, they don't know how often I'm here! We shop at Randall's quite a bit.

Last year, Safeway raised more than $50 million for causes like Breast Cancer, and the Special Olympics. Safeway's executives choose which charities the chain will support. For instance, Safeway's Executive Vice President Larree Renda is also a vice president of the Muscular Dystrophy Association. The grocery chain raised $10 million last year for the charity.

Randall's offers some choice. It allows shoppers to link their rewards card to their favorite charity. And at the end of the year, Randall's will make a donation equal to 1 percent of what was spent on the card. Connie Yates again.

Yates: It's our money, our contribution that we are making, but our customers tell us what matters to them.

But to give, they must shop at Randall's. Stacy Palmer is the editor of The Chronicle of Philanthropy. She says check-out charity programs have become popular during the recession.

Stacy Palmer: Certainly any effort to tie charitable giving to shopping is a growing trend, in part because retailers want to find a way to persuade people to buy.

Palmer says checkout fundraising gives charities access to millions of potential givers. But she says there are drawbacks.

PALMER: When you make a donation in response to direct mail appeal or a telephone thing, they can call you back, they can ask you again and again. And that's really how charities raise a lot of money. So the downside of this for the charity is that they don't have a way to reach you again.

That is, until you need more groceries.

In Austin, I'm Michael May for Marketplace.