Dimensions of the hole that the coins are meant to be inserted through are 3,5 x 0,35 Cm. (Made for the USD, euro, pound, and Czech crowns).
Print at 0,2 mm layer height. 15 % infill will work just fine.
V2
With V1 it is possible to open the puzzle box without completing it properly. I adjusted the model so that this wouldn't be possible.
The author remixed this model.
I edit the model to make it work like a piggy bank. I also scaled it up to 150 % to increase its capacity.