Christians (when they became important enough to be noticed) did not practice sacrifices, which were essential for the Roman religion (it's not about faith, it's about the correct actions, a simple prayer wouldn't do), so the question is moot. Also if you read Pliny's letter to Trajan (written around 112) some things are pretty clear: he has to discover who is and who is not a Christian and he notes this

>Those who denied that they were or had been Christians, when they invoked the gods in words dictated by me, offered prayer with incense and wine to your image, which I had ordered to be brought for this purpose together with statues of the gods, and moreover cursed Christ--none of which those who are really Christians, it is said, can be forced to do--these I thought should be discharged

This is confirmed by other sources: Christians absolutely refused anything to do with the Roman Religion, which as I said was a crime in itself.