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Comment by gs17 | Hacker News Reader

How would you handle things like change on a 1 dollar item with 10% sales tax? I use a dollar and a dime to pay for a coffee refill regularly, and no coins smaller than $0.25 would be messy without forcing prices to go up/down to round evenly or elminating all cash. Rounding to the nearest cent now isn't an issue since sales tax should always be roughly an integer percentage, but rounding to quarters is problematic.

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In Canada, with sales taxes varing from 5% to 15% by province, we round to the nearest nickel on cash transactions. Non-cash transactions are rounded to the nearest penny as usual. Works fine IMO.

Note that the rounding is to the nearest nickel, neither up nor down. So it favours neither buyer nor seller; it all nets out about the same for all in the end.

We stopped minting pennies 10 years ago. They're still legal tender but rare to see since there's no need with 5-cent cash rounding conventions now. There were brief popular grumblings and misplaced arithmetic anxiety leading up to the death of the penny. I expect the same when we bury the nickel and I bet few will miss it either when its time comes. And then the dime.

Of course one can construct amusing temporary edge cases or arbitrage opportunities when buying specific quantities of specifically priced items in the presence of any new rounding rules. The market will respond.

I can't find a proper citation, but rounding is undefined.

The recommended guideline[0] is to round to the nearest 5¢.

This article from 2013 is my closest citation to "undefined behaviour"[1]

> These guidelines are only a suggestion though and there is currently no law that specifies how retailers must round.

I don't know since ~2013 if anything has been decided to make those guidelines "law". I couldn't find anything quickly in the SEO cesspool that is modern web search.

[0] https://www.canada.ca/en/revenue-agency/programs/about-canad... [1] https://cba.ca/phasing-out-the-penny-in-canada

In practise, as a canadian, i have never had a merchant cheat me out of a penny.

But honestly, if it did happen,i doubt i would care.

In practice, as an American, we have a custom of paying merchants to cheat us out of a penny. As in, if a charge come out to $4.99, we hand the cashier a $5 bill and a penny, with the expectation of not receiving change. We also have leave-a-penny-take-a-penny trays by some cash registers with free pennys funded by customer donations.

In Canada, the only people who use specie cash are black marketeers and under-the-table tradespeople, and none of them deal in values under a dollar.

The penny was phased out at the same time people stopped carrying cash, so it wasn't missed.

The US could do what Europe doors and just include the sales tax in the advertised price and arrive at desired prices by leveling things out across the offered inventory.

This approach is too imprecise, you'd constantly be rounding everything up to the nearest dollar -- the net net equates to yet another ripoff against consumers.

We already round up to nearest penny. How do you think I pay 8.75% tax on something that costs $1.99 anyways?

Not the same thing. The USD is a thing, as soon as it becomes the US$100D, we're all screwed.

A) gas prices are in fractions of a cent, and people buy that with cash

B) most items aren't an even dollar anyways

C) I've only once lived anywhere that sales tax was an integer percent

More specifically, you round to nearest quarter, just like we do now for pennies. In your case, the coffee would be a dollar, and if that was too rough on the coffee shop, they could raise prices by $0.10 and you'd pay a dollar and a quarter.

A) A tenth of a cent on a 3 dollar item is pretty far off in scale from up to 24 cents (or 12 if nearest rounding) on a 1 dollar one cent item.

B) Correct, 99 cents would be more likely, which would make the problem worse.

I don't see "prices could go up" as a selling point either (I doubt they'd want to round down unless it let them out of sales tax). How would raising prices to make change differently benefit either of us when you can already pretend to live in your ideal world by just telling places to keep the small change?

Some cashiers hate it when I tell them to keep the change. It throws their count off later if they put it in the register, and they have to count it out themselves if they want to keep it.

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