Here is a reasonably good picture of a set of rolled (and sewn) reins. See where the flat leather has been actually folded and sewn...not simply CUT to make them round.
To tell you the truth, I had never seen cut round leather used until I saw mini harnesses done that way. I cannot imagine any harness maker getting away with such a thing in the regular horse world, as it takes the strength and integrity from the leather to cut it in such a way.