CCTV pictures caught two men binding the woman’s hands and feet using duct tape after forcing her to empty the office safe.
The safe, which was in a back room, contained cash in various currencies.
Detective Constable Johnny Baker said: “These two men used threats and intimidation to coerce the victim to open the safe.
“Although the victim was not injured during this robbery, she has been extremely traumatised by this ordeal.
“I would appeal to anyone who recognises these two men to come forward and speak to police.”
A police statement said the men entered the café around 9 am, shortly after it had opened for the day on 7 April this year.
The first suspect, a black male around 1.83m tall, was wearing a dark hooded top and matching tracksuit bottoms with a cream or white strike down the outside arm and leg. He was carrying a black and yellow ‘JD’ sports bag with a string pull.
Police said suspect two is a slim black male with a goatee beard, wearing an orange fluorescent tabard and a black ‘beanie’ hat.
No arrests have yet been made and enquiries continue.
