Square corners help prevent flutter and rounded corners promote flutter.

If you want to taper you can slice and inlay 1/64 ply into the edge and taper down to it. Make a cutter by screwing a #11 blade down with a shim underneath that is equal to half the thickness of the TE before trimming. Slide the TE across the blade and you have a slot for the 1/64 ply. You can easily taped down to it. Seal it in with thin CA.

Another thing is to taper to a sharp edge, then soak the edge with thin CA to harden the wood.

Personally, I leave mine square.

Here's a photo of the TE of the aileron of a Morris TopCap 3D plane.