The two rocks most commonly made from rounded grains are:

* Conglomerate: This rock is made up of large, rounded gravel-sized fragments cemented together.

* Breccia: This rock is also made up of large fragments, but they are angular, not rounded.

While both are clastic sedimentary rocks (meaning they are formed from fragments of other rocks), the difference in the shape of the fragments is what distinguishes them.

Let me know if you'd like to know more about these rocks!