It's fine to wear casual clothes such as khakis, jeans, tennis shoes, and sandals to many restaurants in Rome. But remember that in Italy, modesty is key. You won't find Romans dining in shorts and tank tops, so keep this in mind for going out to eat, and again, for visiting the sites.
Do locals wear jeans in Italy?
Italians tend to wear basic blue jeans a lot less often than their counterparts elsewhere. It's not that women are always in dresses, and men in suits; it's that when they do throw on trousers, they're rarely basic jeans or khakis. Instead, pants come in a rainbow of colors.