The color video from two angles shows a man in black clothing bursting in the front door just before 8 p.m. Thursday.
The man hopped the counter with a silver gun and apparently ordered the clerk to open the register.
When the clerk gave him the cash drawer, video shows him take the cash as he waves the gun, then runs out the front door to a waiting getaway car.
The video also shows a customer in a yellow shirt whose actions seem unusually calm.
The customer barely flinches when the gunman bursts in and jumps on the counter. He walked toward and right up to the crime in progress, then followed the gunman to the door.
Detectives ask anyone with leads or information to call Crimestoppers anonymously at 305-471-TIPS.