Long winded explanation but I think it's required here. I need to charge VAT only on products within a certain category. So, I created the following calculation and named it "VAT":
([Category]==1)?[TotalPrice] * 0.2:0

Basically if a product is from Category "1" then 20% is added to the total price for that item.

Then, in my Tax rules, I created the following rule and named it "VAT on Bottles":
Trigger:
Number of items with Category of 1 > 0

Calculation:
Based on column subtotal
Subtotal of column VAT plus 0

This works perfectly.

However, I also need to add 20% VAT to the UPS shipping charge. I initially opted for the "include shipping in cart subtotal when calculating sales tax" option in the Shipping rules tab however I quickly realised that because my initial setup is a calculation I can't select "Based on the cart's taxable total" in the "VAT on Bottles" Tax rule.

So, I created another Tax rule and named it "VAT on Shipping" as follows:

Trigger
UPS shipping quote > 0

Calculation
Based on UPS shipping quote value
UPS shipping quote times 0.2

Initially I thought this was working but after looking closely at the figures, I realised that it's not calculating the VAT correctly.

For example, if we have a product in the cart valued at £80.00 then it applies a VAT charge of £16.00 (20%). Perfect.

However, when we add the UPS Shipping to that order, which in this instance is £14.01, it charges an additional £2.30 in VAT making a total VAT charge of £18.30.

20% of £14.01 is £2.802 so it's close to £0.50 short!

I attach my cart files for inspection but let me know what else I need to send.

You can also test this at:
www.nathonjoneswebdesign.co.uk/whiskybroker/

Thank you.
NJ

EDIT: Urggh...the UPS charge already includes VAT so we need to strip out 20% from that and display the fee before VAT, moving the VAT amount into, somehow, the VAT tax charge area.