Can Uber set a round trip fare?
The Guru Take
Uber is an "on demand" service. No "roundtrip" concept.
As Uber is an on-demand service, you request a ride when you need a ride. More recently, there are ways to schedule a ride, but this isn't so much considered a roundtrip, and there are no discounts.
If you would like to make a quick stop, say to pick up a friend, pizza, or something you forgot at a store, you can always ask your driver to wait for you while you are inside. The meter will continue to run and you will owe the driver for the time he or she waits; however, as long as the stop is short, it will be cheaper than requesting another ride and incurring the one-time fees. (This is what's great about Uber. As your identity and your paymenet method are stored in the app, drivers can trust you to not run away without paying.)