Hi folks... struggling with a cut/extrude here.  Any direction / assistance is greatly appreciated!

The attached shows an extrusion.  I'm looking to take the end cross-section and transition it to a 5x5 square millimeters cross-section so that it can be mated to the corresponding component.  I can set the plane and taper the sides in the orthogonal direction, but I can't figure out how to go from the radius of the sides of the cross-section to smoothly transition to a corner of the 5x5 square.

Thank you.

Divya