https://www.npr.org/sections/money/2020/07/14/890435359/is-it-time-to-kill-the-penny

By the 1990s, Kolbe says, he was introducing new legislation to kill the penny with every new session of Congress. But he kept facing resistance — for example, from the speaker of the House at the time, Dennis Hastert, who represented a district in Illinois, the home state of Abraham Lincoln. Lincoln, of course, is on the penny, and Kolbe says that proved to be a major roadblock. So were special interests such as zinc miners and the company that supplies the "penny blanks" used to mint the penny.

Penny defenders' strongest argument was that eliminating it would hurt consumers. All those $9.99 products? The prices would be jacked up to an even $10! They called it the "rounding tax." But Whaples, that penny-researching economist at Wake Forest University, conducted a study of convenience stores and found that the final digit of purchases, which usually involve multiple products and a sales tax, was pretty much random. "And so if you round it to the nearest nickel, the customer wouldn't get gouged," Whaples says. Sometimes you'd round up; other times you'd round down. In the end, it would basically be a wash.