Hemantkumar Maganlal Chauhan, 57, of Newport, was known to his customers as Harry.
He was killed at 7:15 p.m. Friday at the Pen Bantam Market located at 418 Newport Gap Pike.
State Police say Chauhan was confronted by a man armed with a knife.
The suspect jumped behind the counter and demanded money. A struggle ensued and the suspect stabbed Chauhan in the chest.
The assailant then fled on foot with an undisclosed amount of cash.
Chauhan was taken to Christiana Hospital Trauma Center where he was pronounced dead.
Chauhan's nephew, Vikesh, said his uncle always helped his customers.
"He's helping people all the time. Somebody don't have the money, said 'I'll pay later on,' he's always fine with them," said Vikesh Chauhan. "If somebody didn't have the change or was short a dollar, he'd say 'Don't worry about that.'"
Investigators are reviewing surveillance video hoping to identify the armed man.
The suspect is described as a black male who was last seen wearing dark clothing with a mask covering his face.
Anyone with information is asked to contact Delaware State Police at 302-531-5891. Information can also be submitted to Delaware Crime Stoppers at 1-800-TIP-3333 or via the internet at www.tipsubmit.com