Rounded corners issue

Im in a hurry, so don’t give me the “please search before post”-talk. I need to draw a box with rounded corners. I can’t get a hang of it. I want to draw it from the following variables:

boxwidth = 200;
boxheight = 200;
radius = 5;

How do I draw this? You should see the artwork I have (by mistake) created while trying to get it right :stuck_out_tongue: