By default, the amounts are inserted or entered (if manually over-typed) Exclusive of Tax (VAT/GST/Sales tax) on the amount column of the document lines. 

To enter and view amounts Inclusive of Tax (VAT/GST/Sales tax), you may select (tick) the "Default inclusive for documents" field on Stock information (Setup ribbon). 

documents-default-inclusive-tax-setting

You may press the F7 key or click on the F7:Exclusive / F7:Inclusive icons on the "Document entry" screen for unposted documents to toggle between the Inclusive or Exclusive modes.