"That was to misrepresent what he had actually been doing," she told the ACT Magistrates Court on Monday.
Slipper tried three times to have the case dismissed, including once on the grounds of mental illness. But Magistrate Walker ruled the trial should go ahead in the public interest.
The prosecution argued Slipper manually filled out multiple vouchers for single journeys in an attempt to hide the non-parliamentary nature of the trips.
MPs and senators can only use taxpayer funds to pay for official or parliamentary business and the prosecution claimed Slipper knew he was breaking the rules.
Slipper was accompanied by a male staffer on two of the trips and his wife - also on his staff - on one occasion.
On handing down her decision, Magistrate Walker said it wasn't unusual for Slipper to fill out multiple cab charges by hand instead of paying electronically.
But she said his decision to fill out the destinations as "parliament to suburbs" and "suburbs to suburbs" when he was knowingly visiting vineyards well outside Canberra was implausible and dishonest.
"The contents of these vouchers is clearly false," she said.
Slipper's legal team said whether the government incurred any financial loss from their client's actions was in dispute, as were his intentions.
The court was previously told Slipper's life had spiralled into despair as a result of criminal allegations.
In 2013 he twice attempted to take his own life.
His legal team are considering the possibility of appealing against the conviction.
