I don't know where you garden so I don't know when you put your plants out but early in the season it isn't unusual to see what's call Leaf Roll, which is a result of foliage and root mass being out of balance, but that self corrects as the plants mature.

Other than that I pay no attentio at all to leaf curling b'c they'll curl if it's too hot, too cold, too dry or too wet and many hybrid varieties normally have leaves that curl.

If the leaves curl over into a tube like structure then check for aphids.

But unless you see symptoms other than leaf curl, and you say the plants look healthy, I would not worry all that much.

Carolyn

Agree, just Google 'tomato leaf roll' for details and photos to compare to your plants. Or, if the search is working here today, you can search that same term for more discussions on it.

Dave