Sherman spent $727, police prosecutor Sergeant Drew Morrison said.
The victim died on January 26, and her son-in-law reported suspicious activity on her card to BNZ on February 3.
There were 78 fraudulent transactions on the card, adding up to $6740.38.
Atkinson also went through a client's drawers sometime during January and stole a chequebook, Mr Morrison said.
She pleaded guilty to four counts of using a document for pecuniary advantage, and Sherman pleaded guilty to one count.
Sherman told police he needed the money to pay off drug debt.
He has no criminal history, Judge Philip Crayton said.
Judge Crayton sentenced Sherman to nine months' supervision and ordered he pay reparation of $727.
He remanded Atkinson to October 19 for sentencing.