A warehouse man was attacked as two masked men robbed the Co-op supermarket in Waltham Cross.
The raiders hit the victim over the head then grabbed his tie and forced him into an office, where he was forced to open the till on 12 December.
A "substantial" amount of money was stolen by the men who fled via an entrance at the rear of the store.
Both men wore dark clothing. One is described as around 6ft and of large build. The other man was 5ft.
Det Con Richard Venier said: "This was a nasty robbery which has left the victim in shock."