Manual score-and-snap tile cutters make quick work of trimming glazed ceramic tile, but the fresh-cut edge they leave is typically rough and uneven. That isn't a problem if the tile edge will be hidden by baseboard molding or wall tile. But you will want to smooth the rough edge if it goes up against a tub or some other place where it will be exposed.
Hold the tile on edge against a concrete block and rub it back and forth three or four times. Check the smoothness of the edge and repeat, if necessary. Don't have a concrete block? Try rubbing the tile against a concrete surface.