Reports accusing him of doing so were "lies", he told the SABC.
"When I was the HR [human relations] manager I was working under the supervision and authority of executive manager of corporate services and above that was the chief financial officer," he told the national broadcaster.
"So as a ordinary manager I didn't really have any authority."
Mmemezi said he did not sign off on the car allowances.
The Star newspaper reported that he allegedly signed off on the allowance even though he was warned it was against council travel policy.
The allowance for his daughter Nomvuzo Mmemezi was backdated for four years, to a time when she and the others did not qualify for the perk. The allowances for the others were also backdated.
As a result, Mmemezi allegedly violated the council's travel policy, which prohibits junior staff from qualifying for a car allowance. The six had jointly petitioned the municipal manager for the retrospective adjustment.
According to documents seen by the Star, Mmemezi signed off the allowances on May 19 2010.
The Democratic Alliance (DA) on Tuesday said Mmemezi should not be allowed to continue being a provincial minister when he faced serious allegations of irregularities.
"The ANC is denying reports that Gauteng premier, Nomvula Mokonyane, is about to fire Mmemezi, which is very disappointing, as he should have been fired long ago," DA MPL Fred Nel said in a statement.
"He should not only be fired, but there must be full disclosure about the allegations against him, with appropriate sanction where warranted."
Nel said the people of Gauteng had a right to know whether Mmemezi abused his office. This included the alleged misuse of his official credit card and what happened after the accident in his official vehicle.
"We also need to know exactly how much taxpayers' money was wasted and used irregularly, so that it can be recovered from him," said Nel.
"How much longer do we have to wait until he is booted from office?" – Sapa