Hi Larry...so you want a .375" square on one end and a .100" round on the other (like the attached picture)?
To do that you need to use the Loft feature. This requires two sketches. Draw your .375" square then finish the sketch. Then create a parallel offset plane to draw the circle on(if you want a 10degree taper you would need to do a little math to determine how far to offset that plane from the original (.78"). Or if you dont really care about the taper angle, but know the length of the part, offset the plane that far from the original. Draw the circle then finish that sketch. Call the "loft" tool and select each sketch as a section, and it will do a smooth surface transition from the square to the circle. You will need to select if you want the output to be a solid or a surface (I assume solid in your case).
It took me longer to type this than to actually do it.