Police said a man entered the business at 3:15 p.m. and gave an employee a threatening note demanding money.
The man took an unspecified amount of cash and fled, police said.
Munn was arraigned Tuesday before District Justice David Hawbaker in Mercersburg, Pa., police said. He also was arraigned on unspecified charges filed by Waynesboro police, according to the Chambersburg police report.
Munn also was charged Wednesday in the armed robbery of the Leitersburg Pike 7-Eleven on Tuesday, Maryland State Police Sgt. Steve Ganley said.
In that case, Munn was charged with armed robbery with a dangerous weapon, robbery and assault in connection with the robbery, Ganley said.
Ganley said a store video surveillance tape showed the robber tapping the store clerk on the shoulder with a tire iron.
Police said the robber took money drawers and cigarettes from the store at 12:40 a.m. and ran out the back of the store, driving off in a blue car.
The car, its left tires flat, was found nearby on Marsh Pike at Donnybrook Drive. Police said the tires were flattened after the car hit a curb at Leitersburg Pike and Marsh Pike.
The tire iron and cash drawer were in the car, police said.
Washington County Sheriff's Department deputies, state troopers, a state police helicopter and K-9 units from both departments searched for the robber, but did not find him, police said.
During the search, Waynesboro Police Department officers told state police they were looking for a blue car that was missing a mirror. They said the driver lost the mirror after using the car to drive through the front doors of the Save-A-Lot grocery store on South Potomac Street in an attempt to steal money from the ATM inside.
Maryland State Police said the car used by the robber was registered to a man in Waynesboro, Pa. The vehicle registration expired in 2000, police said, but the tags were registered to a car in Gettysburg, Pa.
At about 6 a.m., state police got a tip that a truck was stolen from a home on Leitersburg Pike where the police K-9 trails had ended, Ganley said.
Chambersburg Police Department officers later found Munn in the truck, Ganley alleged.