Photo: Newscast/UIG (Getty Images)

$5 Footlongs. $5 Fill Ups. $5 Lunch Combo. $5 Buck Boxes. What is it about the $5 price tag that compels us to order subs, chicken combos, and pizzas? According to this deep look from USA Today, it’s mostly psychological.

The obvious answer—it’s cheap—isn’t the whole picture. After all, the article notes, fast-food dollar menus and 4-for-$4 options exist. There’s something to $5 that makes consumers think they’re getting a satisfying, full meal, not just a large fries or a few chicken nuggets. Little Caesar’s $5 Hot-N-Ready pizza, for example, has stood the test of time and is the company’s best-selling item, and $5 Footlongs endure despite the fact that Subway franchisees pretty much hate them.

“Psychologically, $5 still seems like not lot of money. It’s just a denomination of a bill,”Ravi Dhar, director of the Center For Customer Insights at the Yale School Of Management, tells USA Today. “It can make it easier than if you’re spending $5.50 and you have to break a $10.”

Chains also say that $5 deals tend to resist inflation, increases in food cost, and other variables. Despite economic fluctuations, both Little Caesar’s and Taco Bell say they have no plans to deviate from the tried-and-true $5 formula. For more insight into why our brains love a good five-buck deal, check out the full USA Today piece.