Round front end:
A small radius will work, you'll find elsewhere here at Ecomodder that 4% of the width is all you need. (About a 3.5" radius for you.)
The rounded edges ensure you're getting smooth flow along the sides. You need that to make the boattail work best.
I've summarized making a brick aerodynamic as rounding the front edges until it doesn't help anymore (should be a 4% radius) then taper the back as much as you can. You'll end up with something like:
