The woman told the robber she was not able to open the till but moved to the next till and put hundreds of dollars into the plastic bag the man was carrying, he said.
The robber then fled the store and ran off down Jellicoe St.
Mr Gillgren said he did not know whether the man had a getaway car but no one else was in the store at the time of the robbery.
The woman at the centre of the terrifying ordeal did everything right, Mr Gillgren said.
''I am very proud of her.''
The robbery was captured on CCTV footage and a still picture of the alleged offender has been attached to the shop counter.
Mr Gillgren and his wife Tina Gillgren-Bosch who had owned the store since June last year were asking customers coming in to the store to help identify the man.
The robbery is the latest in a recent spate of armed robberies across the region.
Mr Gillgren said the robbery had not been unexpected.
"Given the number of recent robberies at dairies and similar stores it was always a case of when not if we would be targeted."
Anyone with any information which may assist police to locate the alleged offender should phone Tauranga police station on 07-577 4300.
Alternatively information can be provided anonymously via the Crimestopppers line on 0800 555 111.