There are merely 2 cash registers you need to use for this achievement, both in the hub area of Gilly Island. Jump and press X to activate them.
The first is directly in front of you from where you start, to the right of the "Secure the Talent" level door in the banana stand.
The second is off to the left side over a bridge, on the bar counter to the left of the "Stuck in Paradise" level door. Jump and press X again to get the achievement.