Tau told the dairy owner he had to grab his wallet and left but returned within a minute and handed over a $5 note.
He then grabbed a bag of confectionery, reached into a plastic bag and pulled out a hammer.
He lifted the weapon up above his head and told the owner "give me all the money", the summary of facts for the case said.
The dairy owner attempted to push Tau away but the robber switched the hammer to his left hand and pulled the till towards him. He then opened the till and removed $270 in notes before running from the dairy.
When arrested, Tau admitted robbing the dairy and said he was drunk at the time.
The dairy owner has sought reparation of $270.
Tau will be sentenced on July 17. The charge carries a maximum penalty of 14 years in jail.