See the below example of a tax calculation:
If an item was 10$ with 20% tax, the cost without tax would be 8.33$, which is why it gives 1.67$ as 20%.
The total amount is inclusive of tax, and to find the amount without tax you would divide by 1.2 (percentage of tax) i.e. 10/1.2 = 8.33
If you still believe this is wrong after manually calculating, raise a case and provide:
Screenshot of the expense submission and the tax figure calculated.
Confirm the tax figure selected.