He was convicted and remanded on bail until his sentencing in June.
Fallon has no previous convictions, the court heard.
Superintendent Karyn Malthus, the Auckland City District Commander, told the Herald in a statement that Fallon is currently a sworn police officer, holding the rank of constable.
She said the officer had been charged with tax-related crimes by the Inland Revenue Department (IRD) and was not the subject of any police investigation.
"An internal employment investigation will be conducted pending the outcome of this matter in court," she said.
Police were unable to comment further while the case remained before the courts.
An IRD spokesman also said he couldn't comment on the case, citing taxpayer secrecy provisions in legislation.