If there was a cash register on your grocery cart, would you spend more or less? Real-time feedback on how much they're spending leads budget shoppers to spend even more.

One third of Americans shop for groceries on a budget. They also worry about going over their budget. A new study in Atlanta grocery stores shows that smart shopping carts – carts that display the total price in a shopping cart – increased both a budget shoppers' confidence and how much they purchased.

The study further found that when shoppers know exactly how much they're spending, they were more likely to splurge on items like chocolate and brand name cookies, and even though they spent an average of almost 22% more, they left the store happier than those who did not receive this feedback.

But this real-time shopping feedback actually leads non-budget shoppers to be more frugal.  On average, they spend 19% less, and purchase fewer national brands and more of the less-expensive store brands.

"Real-time spending feedback enables budget shoppers to spend more of their budget and feel good about it," says Koert van Ittersum, professor of marketing and consumer well-being at the University of Groningen in the Netherlands. "It makes people smarter shoppers, but that doesn't always mean they'll buy less."

Smart carts lead budget shoppers to spend more and feel better about it, but they lead non-budget shoppers to be more frugal.