I live in the United States, and many of our ATMs only dispense money in $20 increments. This makes sense given the added infrastructure that would be required in the machines to dispense many different kinds of bills or coins, and that $20 is a good amount of money but not that much.
At almost every ATM I've seen, when given a free text field to enter a value for withdrawal, the user must enter the full value, including cents. For example, to withdraw $20, the user must type     (with the decimal point implied before the last two digits entered). Why is this? Aren't those two last zeros entirely unnecessary?
The only other reason I can think of is that since most ATMs have transaction limits of $200-500 or so, users can't remove $2,000 in a transaction, and so by including the extra decimal places you're making the user think a bit more while entering the number, and the machine won't do anything if the user enters an incorrect value. But I'm not convinced that's the reason why.