Custom field that will compute for the sum of the item's rate and VAT amount per line item in the Sales Order

1.Navigate to Customization > Lists, Records, & Fields > Transaction Line Fields > New.
2.Enter the Label of the custom field.
3.Select Currency in the Type dropdown.
4.Do not check the Store Value check box.
5. Under Applies To > Check the Sale Item check box.
6. Under Validation & Defaulting > Default Value: ({rate}+{tax1amt}) and check the Formula check box.
7.Click Save.

Note: 
1. This will only apply to NetSuite UK Edition.  Tax Amount is the VAT Amount.
2. By default, Tax Amount Column set to show in the form.