The incident happened at the McColls store in Hirst Gate, Mexborough, at around 9.30pm on Wednesday December 28.
After stealing cash, the man left the store and drove off in a white Ford Transit van, thought to have been parked nearby.
Officers are keen to speak to the man in the CCTV image in connection with the incident.
Anyone with information is asked to call 101 or email [email protected] quoting incident number 988 of 28 December 2016.
Information can also be passed to Crimestoppers anonymously on 0800 555111.