Well, it is super useful do be able to do exact arithmetic. For example, to not get scammed when you buy anything, or share a bill. I've seen American university students who don't know how to compute a percentage of a given amount - so I'm not very impressed by common core math to be honest.
That being said, it's probably a cultural thing too. I noticed that in the USA (at least in California?) it is customary to exclude the taxes from the price that is displayed on the price tag. Since the tax rate is different for different products, it's pretty hard to compute the actual price that you pay, and in practice you just take whatever you need and don't have an idea what you pay. In addition, it is not very usual to split the bill (I'm not talking about simply dividing the price by the number of people, but about actually computing the price of the stuff you ate, and not paying more than that).
When I go to the grocery store, I usually keep a sum of the price in my head while I pick products. That way I'll know if something is off at the counter.
That being said, it's probably a cultural thing too. I noticed that in the USA (at least in California?) it is customary to exclude the taxes from the price that is displayed on the price tag. Since the tax rate is different for different products, it's pretty hard to compute the actual price that you pay, and in practice you just take whatever you need and don't have an idea what you pay. In addition, it is not very usual to split the bill (I'm not talking about simply dividing the price by the number of people, but about actually computing the price of the stuff you ate, and not paying more than that).
When I go to the grocery store, I usually keep a sum of the price in my head while I pick products. That way I'll know if something is off at the counter.