Wait first thing when you say multiplayer, are you talking about an online multiplayer game using the multiplayer object or a local multiplayer game? Synced objects may have issues with pin if the host and peer do not agree on where the object should be. However, labels and such generally have no need to be synced at all, just displayed and updated locally on each peer, which should be smooth.
It's difficult to help with limited information without actually seeing the project or your problem.
Pixel rounding is a project property. Try turning it off if it's on.