Use any emergency vehicle, turn on the sirens, and drive (speed does not matter). The booth attendant will open the gate and you will have saved $5.

When in a car or a motorcycle, drive up to toll booth. Stay on the far side of the booth. Niko will stick his arm out, but not put money in the basket. The gate will still open.

Ride a motorcycle to the side of the pay toll wall. You will not pay a toll if you can drive through the small gap on the sides.