I have tried the following methods to create rectangles with rounded corners:
 Use spline tool
 Import rectangle from Inkscape (native tool to round rectangle corners)
 Create a rectangle, remove corners with smaller alpha over rectangles, overlap a circle over each removed corner so 1/4 of the circle creates the rounded corner
Problems:
 Cannot get the sharp curved look of a circle (like method #3), is there a way to do this?
Spline rectangle before tangents
Spline with tangents moved
Corner looks uneven (compared to final picture at bottom from method 3

The rectangle imports without the rounded edges, is there a way to do this?

Messy to manipulate
Rectangle without corners
Add circles
Final look