I think consumers would love having baked in taxes and clear prices and were the government functional I'd hope that a consumer advocacy agency could enforce this - but that's simply not where we are right now.
Lots of odd American customs can be explained by this phenomenon. The other major difference in the states is that we don’t have many places that only have federal taxes. States and every locality from the county to the water reclamation board can have tax authority. Those 2 things in conjunction go a long way to explain the differences you see in US tax treatment.
By comparison, in Japan the consumption tax is 10% for most items (8% for groceries and takeout), and it's the same nationwide.
In addition, there are sometimes fees that are prohibited by law from being baked in. For example, California has a statewide ban on free "single-use" bags in grocery stores and some other businesses. These businesses are required to charge their customers for bags, and they are not allowed to bake it into the price. Some municipalities have extended this to disposable cups as part of an effort to discourage them in favor of reusable cups. For example, Santa Cruz mandates a 25 cent fee on disposable cups. The Costco $1.50 hot dog + drink combo is normally $1.50 + sales tax, but in Santa Cruz it's $1.50 + $.25 mandatory cup fee + sales tax (yes, the cup is taxable). I have yet to see someone bring a disposable cup to Costco or to other places where paper cups are sold, however.
Having baked-in taxes will require big changes about how taxes and fees work in America, the land of extra sales taxes, extra fees, surcharges, and tipping.
I think most of the ones from previous years are all in people's junk drawers, couches, etc., and only go back into circulation when someone decides to dump them into a Coinstar machine. Retailers are already reporting shortages.
So while the mil isn't really used anywhere else that regular people see any more due to inflation, it is a valid division of the dollar and that's why they are able to get away with it.
No, it's purely stylistic. We tend to spell out denominations on coinage and "dime" is just the American spelling of disme, meaning a tenth.
The capped bust dime from 1809-1839 had "10 C." rather than "One Dime". Similarly, the capped bust quarter said "25 C." instead of the modern "Quarter Dollar", the half dollar said "50 C." rather than the later "Half Dollar" and the half dime said "5 C." rather than the later "Half Dime."
Most of the 18th century and early 19th century coinage, besides half pennies and pennies didn't have their denomination written on them at all.
When the final calculation of XX.YYY litres * AAA.9 pence/litre is done, it's then rounded off to 1 pence.
Currency conversions are also frequently done with readers that aren't a round multiple of pence, even in official government tables: https://www.trade-tariff.service.gov.uk/exchange_rates/view/...
They're allowed to get away with it because of a dysfunctional lobbying driven government. Mils don't exist in the common knowledge and if any reasonable person looked at this they'd call it out. It is useful in accounting but a Mill has never been minted and the last half penny was minted in 1857. It has never been possible using issued physical legal tender in the US to pay a debt of $3.129
The Mill doesn't exist because of some archaic need - it's pure dysfunction and the utilization of it in gas prices is a practice that should and very easily could be made illegal.
$4.999 looks a lot smaller than $5.00 to everyday people and it makes the gas company more money than $4.99. That's all there is to it.
1: https://www.cbsnews.com/minnesota/news/why-do-gas-prices-alw...
2. https://www.cnn.com/2022/06/14/energy/why-gas-prices-fractio...
So I don't think it's just "evil retailer tricks".
We unofficially drop the coins/bills when the reach ~US$0.03, so now we dropped the AR$50 bills and everythig in cash is rounded down to AR$100 (US$0.07).
(The only exception is the photocopy shop 2 blocks away from home.)
Credit cards are charged the exact ammount, with cents that are irrelevant.