[john.gersh]

An easy way to do this is by using Edit>Shapes>Union Shapes. Make a rounded rectangle with the desired corner radius. Cover the corners you want to remain square with smaller rectangles whose edges are aligned with first one. (Smart alignment guides are a great help here.) Select all the shapes and create the union. To get corners with different radii, give the background rectangle the larger radius and the covering ones the smaller. A similar process works for other shapes, but it's slightly more complicated. If the shape is not a regular polygon, make the corner-covering shapes by duplicating the original and shrinking the copy in order to keep the corner angles the same.