Muawaz Khalid and Nabeel Shafi attacked Gurmail at his Cowcliffe store in Huddersfield during a robbery in February. He died as a result of several blows to the head.
Three other men involved in the incident were cleared of murder, but were found guilty of robbery and assisting an offender. Sentencing has been adjourned until November 16.
The verdict came as the Sentencing Council launched a consultation on potential changes to sentences handed down for violence against shopworkers. It proposes a specific framework that can be easily applied to crimes of varying severity, taking into account the harm caused to the victim and the circumstances of the offender. The consultation is open to submissions until January 5, 2011.
Association of Convenience Stores chief executive James Lowman said: "We will respond to the consultation and ensure that custodial sentences remain for the worst cases."