From Monkey Island wiki
Pinchpenny Island is a small island mentioned in Escape from Monkey Island. It is depicted on the map of the Tri-Island Area, which shows it to be located roughly halfway between Lucre Island and Phatt Island. From the map it appears slightly smaller than Lucre, and slightly larger than Phatt.
No other reference is made to Pinchpenny Island at any point in the series and the player never has an opportunity to visit it.