Is there a shader that can be used on material level that will give the effect of round edges when assigned to an object? I'm not looking to increase the mesh density, I remember in 3DS Max, Mental Ray, round corners is an option that can be enabled in material, so the object's sharp edges will "look" like smooth, without changing the object's mesh, is there a way to do this in Cycles?
A straightforward solution has been added to the most recent Blender distributions (after the released version of 2.79b, so you must download newer updates of 2.79b, or 2.80 Alpha, from https://builder.blender.org/download/ to enable it).
There's a single node (Input > Bevel) that fakes bevelled normals. Of course it won't change the geometry, so it doesn't look great from too close, but it can enhance pretty convincingly the specular/reflection at the edges.
I figured out how to do this with a specularity map (kind of).
The limitations are apparent as you look at the focal center of this image, the edges look rounded. However, the corners don't actually change their geometry as seen at the extremities of the geometry.
Which actually led me to this thought - If a spec map can influence this, then so can generated Ambient Occlusion (Pointiness), see the following:
Both cases being, that the first option would be necessary when there are external angles of pointiness, and the second option being, when there are internal angle by which AO/Pointiness will give you this spec map like result.