You can use the Round tool to convert a line path to a rounded corner. If no corners are selected, you can manually click single corners to round off the edges. The conversions will only be done when applied to paths. (Convert an object to paths by choosing Extra > Convert to Path.)
How to round off corner edges
1. Select the corners you want to round off with the Direct Selection tool.
2. Select the Round tool from the Tools panel.
3. Enter the distance in the control panel.
4. Click Apply.
Using the Sharpen tool , you can convert multiple consecutive lines and beziers in one path to a point.
This point straightens the paths in between.