In The Netherlands I also have a coin jar. I pay for everything with my contactless card or smartphone. I have a 20 euro bill in my jacket pocket for when I encounter a shop where I can not pay digitally. So I use that bill, but then end up with a bunch of coins. Coins are heavy and jiggle around in my jacket pocket, so at home I dump them in a jar. And then I get a fresh 20 euro bill from inventory and put it in my jacket pocket.

Every now and then I go to the local marketplace at the city square and exchange my coin jar for a stack of bills. They usually have to pay for the coins so it's a beneficial exchange for us both.