The Cashier is a character that appears in the episode "Jailbreak!" He was only seen during a flashback of the Purple Cellmate.
The Cashier is a tall, light orange fish with black, fuzzy hair, and has light teal fins, and also has dark orange lips and eyelids. He also had buck teeth (much like SpongeBob's) and wore a white hat and a white shirt.
The Cashier was first seen reading a magazine called "Video Games" in the Grab-it Mart. He was scared into giving all of his money to the Purple Cellmate hoping not to see anymore of his "disgusting features."
The Cashier's role is pretty similar to Squidward's, as they both are cashiers and read magazines during their shifts.
Humorously, the Cashier was scared off by the Purple Cellmate whose face greatly resembled Squidward's at the time.