Pagan to Christian
As the Roman empire transitioned from pagan to Christian, the art transitioned as well. Some of our later coins show Christian iconography like crosses and the face of Jesus. Constantine was the first emperor to allow Christianity and the first to feature a few small crosses on some of his issued coins.
After time, pagan iconography was functionally replaced with Christian art. Interestingly, however, much of the Christian art closely resembles its pagan predecessor. Christianity did not develop its own distinctive style until much later in the Roman empire.
The face of Jesus on the last coin in this list is similar to the practice of picturing Zeus on coins. The style is the same but the deities have been exchanged.