Is there a way to override the automatic tax calculation in an Expense?

Use cases:

(1) If the expense is for a meal, there may be a gratuity included in the value that the user inputs -- so the automatic tax calculation should not be on the full value.

(2) If the expense is for a meal with alcohol, here in Canada there may be 3 taxes on the receipt: an alcohol tax, a provincial tax, and a federal tax. There is no real way to create tax codes that will properly record these. A manual input field to override the tax calculation would be helpful.