If you usually use a vending machine... do you:

1)Make your selection first, then put in exact amount cause you don't truse the machine.

2)Make your selection first, then put in whatever you have that adds up to that ammount, if it goes over thats ok the machine gives change

3)Put in as much change as you have, see what it adds up to then make your selection based on what the machine says you have in change, then get your change after the product is despenced.

4)Other, englighten us.