Spellbinding Boxes

You borrow a quarter from a spectator and have them initial it. You then cover the coin with a cloth and let them hold it. While they are holding it, you bring out a shiny brass box and set it down in full view. The cloth is pulled away showing the coin has vanished! It gets better. They are told to open the brass box. When they do, they find inside another brass box, then another inside that one. Finally after four boxes they find their signed coin inside! It looks impossible!