Maybe we could redefine the quarter to be worth 20 cents? You could take 4 quarters to the bank, and get back 5 with "20" stamped on them. Machines that accept quarters just need to tweak the quantity. It'd be nice to have a smaller 50-cent coin also.
Why would it be best, considering the enormous cost of replacing 25 cent coins with 20 cent coins? What advantage does 20 cent coins have over 25 cent coins?
Because it lets you round prices to 10 cents (drop a digit), rather than 5.
Technically you'd have to round to 20 cents, since you can't get 10, 30, 50 etc. cents from 20s.