The last-ever penny will be minted today in Philadelphia

Nickles are likely to go shortly after. You can do everything you can with nickles with dimes and quarters, nickles have worse economics than pennies, and have had their minting suppressed below the market needs for years. Once pennies leave circulation, the problems with nickles will become urgent and they'll quickly leave.

Dimes are small and cheap to make though, so they'll probably stick around.

It's impractical to eliminate the nickel and penny, while keeping the quarter and dime. The most practical way forward is to keep only the dime, but people will be quite upset about the loss of the quarter.

It might be a little bit cumbersome, but I don't think it's impractical.

With only quarters and dimes it's difficult to pay $0.05 or $0.15, but it's possible. If I owe you $0.05, I must give you a quarter and you give me two dimes. Or I give you a $20, you give me $19 in paper money, three quarters and two dimes. If I owe you $0.15, I must give you a quarter and you give me one dime. If I owe you $0.95, I can't give you $1 and get change, I'd need to give you $1.25 and get three dimes back. Or give you $2, get three quarters and three dimes. Owing $19.95 or $19.85 would be most inconvenient, since many people seem to live life with only $20 bills in their wallet and there would be a lot of extra change required.

But, if we stopped minting pennies because they cost too much (3.7 cents), it's hard to imagine we're going to keep producing nickels when they cost 13.8 cents to mint. Dimes are much cheaper than nickels (5.8 cents), and quarters aren't too bad relative to face value (14.7 cents). Article with values [1], which I rounded to millidollars. I'd bet people would rather keep dimes than quarters, but rounding everything to quarters is a big step. I certainly would prefer quarters --- it's been a long time since arcade machines took dimes, and I only have quarter mechs (most of my games are on free play, and I can reuse the quarters I need forever, or add a credit button, but still).

[1] https://www.nbcphiladelphia.com/news/national-international/...

Rounding to a nickel has the advantage that's it's both simple (1, 2, 6, and 7 round down; 3, 4, 8, and 9 round up) and fair (there's no systematic bias in favor of the buyer or seller).

Dimes need to deal with how to round numbers ending in 5, making them unfair, or (with a more elaborate system of looking at both digits) complicated.

Quarters (being an odd value) are fair, but kind of a nightmare to memorize all of the values that round up or down (1–12, 26–37, 51–62, and 76–87 round down; 13–24, 38–49, 63–74, and 88–99 round up; and I'm not even sure I don't have an error in those numbers).

Also it's awkward if a higher-valued coin (e.g. quarters) isn't divisible by the least valuable coin (e.g. a dime)