When you apply a contour to an object, by default CorelDRAW will apply Mitered corners to it. There are two other options available to choose other than Mitered; Round and Bevel. When a contour object is selected, you will see   button on property bar. Clicking on the button will reveal options to toggle between Mitered, Round or Bevel corners.

Tip provided by Pratik Shah, CorelDRAW Master, graphic designer