This window is used to override the job tax rate only for the detail line you are currently working on.  As an example, this might be...

Sharpe News Quarterly Construction News Inside... FDM Contracting Finds a Work/Life Balance with SharpeSoft. Introducing the SharpeSoft...

Key windows and tables throughout the system, especially those that contain long lists of entries (e.g. Jobs, Vendors, Owners and Item...