Taper Face

The Taper tool used to turn a straight edge into a tapered edge.  This tool will taper the entire face you select, not create a taper on the face itself.  To use this tool, click the icon and select the face you wish to taper.  Next create the Taper line by selecting the first and second points of the line.  This line is outlined to the right in Cyan.  This will be the reference line for the Taper, and the line from which the Taper angle is measured.  Lastly, enter the angle of how much you want to taper by.

 
* Special Note: used in simple applications like this, the Taper Face tool and Rotate Face tool are very similar in function and in result. If you compare the Taper Face and Rotate Face images, the only difference is the orientation of the line that is used in the command.  In the Taper Face tool, the line is selected such that the face is tapered along (or with respect to) the line.  In the Rotate Face tool, the line is selected such that the face rotates around it.