THIS. ^^^^Lying is illegal. You lie, then expect a slew of charges coming your way.
"However," you are not required to answer their question directly either.
When you say that "you have nothing illegal in the vehicle." That shuts down probable cause for a search, because you are not doing anything wrong.
If there is some type of over-riding factor, like large amounts of blood over the car seats, hand grenades in the passenger seat, the smell of marijuana/alcohol emanating from your vehicle, then you are under the magnifying glass, so mind your P's and Q's.
I have nothing illegal in my vehicle.
Sent from the 3rd Rock