You'd need to clarify what constitutes an "input" in physical cash
It is simple: a single input, or a single output, can be called "a coin". The main difference between fiat currencies and crypto, is that you can use any denominations you want. Which means, that if you would have a consensus rule, that "only coins with equal amounts, starting from 1, 2, and 5 are valid", then it would be a perfect soft-fork, and would recreate the
change-making problem.
Some example: transaction fc406eb3fa4a3f305f5670880b9bc69aeed89b2756dd9eb34e7359c21969dcce, you give three coins to the shop: 9232, 9201 and 9110 satoshis. You pay for example 14460 satoshis, and keep 2931 satoshis as your change (or the other way around). And you also pay 10152 satoshis to the government, for keeping the currency alive.
Also, this analogy is even more relevant, when you think about how easy is to use a coin. Because you can pay with a single $100 bill, and then it is just a light piece of paper. But you can also bring a huge bag of 10,000 pennies, and put it on the table, in front of some cashier. Then, the amount will be the same, but if you think about resources, needed to process your transaction, then they will be bigger, and you will probably pay a bigger fee for wasting someone's time to count all of those single coins, and for forcing all people in the queue to wait for "confirmation".