Prompt line > Grid and Snap panel > Percent Snap
Percent Snap increments scaling of objects by the specified percentage.
Interface
The snap percent increment is set in the Grid and Snap Settings dialog. The default is 10 percent. Right-click the Percent Snap button to display the Grid and Snap Settings dialog.
This is a general-purpose snap system that applies to any operation involving a percentage, such as scaling or squashing.