Write the next sentence in the following story.

How to tip a cab driver
Listen for the fare.
When the trip is over, the driver will tell you how much you owe. Calculate the tip as a percentage of this fare, or " eyeball " the amount by rounding up to the nearest $5 or $10 bill increment.
Most cabs feature a fare ticker which allows you to watch the price of the ride rise as you approach your destination. If you're in a hurry, you can use this to predict, calculate, and prepare your tip before it's time to get out of the cab.