You can give the Uber driver an amount by rounding off like, if the charge is 6.5$, then you can offer 10$ and tell the person to keep the rest of the amount as a tip. Similarly, if the bill amount is 15.3$, you can give the Uber driver 20$ and convey the person to keep the change.
So, if the bill amount is small and close to an even amount, you can use this trick, and if the amount is large, or has to be split between friends use, our tool Uber tip calculator.'