The woman was working at Mannin News and Wine on Westgate when a man attacked her and stole the contents of the till at 5.45pm on Wednesday.
She was taken to hospital for treatment for her injuries but has since been discharged.
Detective Sergeant Andy Shields, of South Yorkshire Police, said: "We are in the early stages of the investigation and are conducting numerous enquiries in relation to the incident.
"The victim attended hospital but has since returned home after treatment for her injuries.
"I would urge anyone who may have been in the area at the time or who may have witnessed the robbery to please come forward."
In September 2016, a woman was attacked during a robbery at another newsagents on the same street.
Judith Ducker, aged 64, was left with a fractured skull, fractured eye socket, multiple head lacerations and bruising to the brain during a robbery at Westgate News.
Her attacker - Paul Storm Blueitt, 36, of Cambridge Crescent, East Dene, Rotherham - fled with £40.
He was found guilty after a trial, sentenced to life behind bars and ordered to serve a minimum of 27 years before he can be considered for parole.
Mrs Ducker, who was fighting cancer at the time of the attack, was never well enough afterwards to receive further treatment and the cancer spread.
She died the following month.
Anyone with information on the latest incident should call South Yorkshire Police on 101 and quote incident number 803 of January 10 or Crimestoppers on 0800 555111.