From the Model Rocket Handbook, showing nose cone shapes not fins, a perfectly squared off leading shape has high drag, however with slightly rounded edges the drag drops to about 30% more than a perfect parabola shape. Likewise, from elsewhere, as long as laminar flow can be maintained a full trailing airfoil shape is great but as soon as there is turbulence, you can cut it off square right there without increasing drag (also, rounded trailing edge shape doesn't really help anything). So, I make sure the leading edges are least rounded a bit, and sand the trailing edges some at an angle. Never much more for ruggedness.
Rounding the trailing edge of fins greatly reduces the Base Drag on the model. We still have a good be from the motor but rounding those trailing edges helps. Also reduces the landing damage.