Police and hospital officials said six attackers used handguns fitted with silencers during the heist in Fallujah, 40 miles (65 kilometers) west of Baghdad.
The victims were believed to have been the owners of the shop, police said.
All officials spoke on condition of anonymity because they were not authorized to speak to the media.
Street crime appears to be soaring in Iraq as sectarian fighting wanes and the US military prepares to withdraw its forces by the end of next year. Criminals and insurgents are exploiting security gaps as Iraqi politicians bicker over the formation of a new government more than three months after national elections.
None of Iraq's main political groups won a clear majority in the March 7 vote and parliament has met only once since then. Parliament is scheduled to meet next July 14.
An Al-Qaeda front group claimed responsibility for last week's strike on the Central Bank of Iraq, in which at least 26 died. On June 9, gunmen killed three jewelers before fleeing with gold in southern city of Basra. Two weeks earlier, a similar robbery in Baghdad left 15 dead.
