The reason supermarkets offered cash back was that this allowed them to massively reduce the amount of cash held on site and thus reduce their insurance costs.
But wouldn’t this increase the amount of cash you need on hand to ensure you can make change and now give cash back?
I’m not sure they even offer cash back these days, it has been so long since I asked, and the number of cash transactions has dropped massively over the last few years.
Anything under 10 cents gets rounded down/up accordingly
It doesn't matter. Minting and transporting it, even in your pocket costs more than you'll ever get in dealing a more "precise" denomination
The US used to have a half-penny coin. It stopped being minted in 1857.
The purchasing power of the half-penny at the time was about as much as a quarter has today.
It wouldn't be crazy to get rid of all coins worth less than 25¢ and round all purchases to the nearest quarter.
Obligatory CGP Grey: https://youtu.be/y5UT04p5f7U
Think about the last time you bought some for $1.27 and paid with a $20 and they took it without blinking.
I live in a developing country where there are still a ton of small mom & pop shops that aren't willing to eat the cost of that externality. So it isn't uncommon to go to one of them and they'll go "sorry, I can't make change for that bill size". Then you suddenly have the hassle of needing to drive to another store or getting change somewhere else or whatever.
In practice you adapt: the ATM only spits out big bills so you make a purchase somewhere to start breaking them up. Go buy a soda at an international chain instead of the local corner store. That kind of thing.
But it is still a cost we all pay, since "making change" isn't free.
An anecdote: during COVID people had to use shopping carts in the supermarket (social distancin). Those trolleys needed a 1 euro coin inserted in them to unlock. Chaos ensued because many customers were not carrying cash- let alone coins.