If you're going to do a rounded corner like in your image you can fillet the corners and set the radius to be half the thickness of the line width. The outside corner of the line will be rounded however the inside corner will not.
I've noticed if one of the two segments is an arc then the corner will not have the nice mitered corner your looking for. If you a short line segment at the end of the arc segement then you will get the nice mitered corner when you join and'or fillet.
Access a broad range of knowledge to help get the most out of your products and services.