Taxis are plentiful in Rome, even late at night. Even if you don't speak Italian, if you show the driver the address, they will be able to get you to the right place. Many of them use a GPS device. Any taxi ride I have taken within the city center has been in the range of 10-15 euro (and that's usually one end to the other). You will be charged a little extra if you have luggage or if you are traveling at night.
For the most part, I have have good experiences taxi drivers in Rome. They are honest and proud of their city. And we try to work through the language barrier together. There are two places I have run into dishonest practices 1. taxis parked within Vatican City that don't have a meter 2. Getting a taxi at Termini, even in the taxi line. Sometimes the men who are "calling" the taxis (who I don't think actually work at Termini) have tried to tell me "oh prices are more expensive today because streets are closed, etc". But when I make it clear I don't believe them, they wave me on and I just get into a taxi and make sure they turn on the meter.
I think you can use the Uber app to price out a trip within Rome without calling the actual Uber. If you know the address/name of the hotel you are staying, you can see how much you would be charged for trips to various tourist places.