It all depends on the type of loading on the construction ; for static loads a fillet weld can withstand a lot of forces, so you don't need to chamfer the rod. But for dynamic loads and bending one can prefer chamfering to obtain perfect penetration, resulting in a better flow of forces through the workpiece.
But the weld volume can cause distortion on your plate. So there's another method to obtain good penetration : drill a hole (diameter (1/2" + 3/16")) through the plate; chamfer the hole with a special bore. You can chamfer both sides (half X-groove) or only one side (half V-groove). If you prefer a V-groove, chamfer the bottom of the plate.
Set the rod through the plate and weld it together. The weld volume is now concentrated into the plate; resulting in less distortion (in the other case the volume is welded into the rod and on to your plate, resulting in stress and distortion)
Good luck.