The crook, who was wearing a mask, struck at the Co-op on High Street, Ecclesfield, at 5.50pm on Sunday.
A South Yorkshire Police spokesman said he forced staff into a room where the safe is stored.
He added: "At approximately 5.50pm on Sunday, January 21, a male entered the Co-op store on High Street, Ecclesfield.
"He was wearing a mask and carrying what was described as a machete.
"He forced staff into a rear room where the safe is located and was subsequently opened.
"The offender stole £3,000 from within and made good his escape out of a rear exit."
Anyone with information should call South Yorkshire Police on 101 or Crimestoppers on 0800 555111.