Rounded corners give a soft, adobe-like look to a room and a more finished look to trimless open doorways. Making a rounded, or bullnose, corner is easy if you plan for them before installing drywall. It's as simple as changing the kind of corner bead you use for the project. You'll also need to cut the sheets of drywall a bit short so they don't overlap at the corners; otherwise, the drywall will kick out the rounded corner bead and it won't rest against the surface properly.
You can find rounded corner bead at most home centers and lumberyards. There are two varieties: the all-metal, nail-on type and the metal with a paper face. I prefer the no-nailing, paper-face type because it's faster, more user-friendly and more resistant to chipping than the bare metal. Apply it the same way you would ordinary drywall tape. Lay down a base coat of joint compound, embed the paper from the corner bead in the wet compound, and
apply a topcoat.