It's so easy to use coins, pennies included, in day-to-day transactions I never accumulate any. Accumulating pennies or other coins is a concept I don't understand. You can spend up to 4 pennies in any purchase you do, and if you don't can't never receive more than 4. For nickels, dimes, and quarters, the maximum is smaller.
If a person has good basic arithmetic skills and it is a priority for them, then yes they can use coins easily. However, a lot of people either can't do the math or are unwilling to use change correctly.
For myself, it's such a priority that I'll get upset with myself if I have more than 4 pennies.
Japan has more coins (in regular use) than USA, so giving the correct amount is even more important or you'll end up carrying a lot of coins. 1000 yen is the smallest bill so... Example: 999 yen. 500,4x100,50,4x10,5,4x1 yen coins, 19 coins total.
When I used to use cash I used to do this all the time. I would nearly always overpay to minimise the number of coins in my pocket. For example I had a bill of £1.63 and I was paying with two £1 coins, I would get 37 pence in change, which would be a minimum of four coins (20p, 10p, 5p, 2p). So I would pay £2.13 to get a 50p or £2.03 to get two 20p coins.
95% of the time the person serving me would clock on to what I was doing but the other 6% it'd take some persuasion, and occasionally they would insist on giving me back my overpayment before ringing it up.
Most of our supermarkets have at least one self service machine that accepts change. Once a week I pour any loose change in then settle the rest with a card.
When I lived in Scotland there was a "loose change" machine at the local Tesco. You pour in your coins and it would give you a receipt you could take to a cashier to get cash back - but the downside was that it charged you something like 10% of the total as a fee. Which I wouldn't pay.
Edit: I just searched and the Tesco documentation says "There is a 25p transaction fee and an 11.5% processing fee on the total amount of coins you put in the Coinstar centre. For charity donations, this processing fee is reduced to 8.9%." (wow, how generous!)
Back in the day, I'd sift through my jar of change and keep the quarters, which were good for parking meters and laundry. The rest went into the Coinstar machine. The fee for counting dimes, nickles, and pennies seemed OK.
The machine always had some weird foreign coins or subway tokens left over by the previous customer in the reject bin, which was potentially interesting.
*You don't think I'd go into combat with loose change in my pocket, do you?"
But I must admit that I never formed the habit of bringing change with me when I go somewhere. So it piled up at home. The quarters were easy: They got saved for parking, laundry, etc. But I ended up with a sack of pennies that I finally cashed in at the bank.
