There seems to be something very strange and confusing going on with the total display of your shopping cart.
Being a UK store by default everything has VAT (20%) on top. So all products sold and all shipping is subject to VAT.
Now I have added one product that is £3.48 inc VAT
For the purpose of showing what is happening I have included all fields possible. The total control shows as such.
Sub Total: £3.48
Shipping: (inc vat) £0.00
Tax: £0.58
Total: £3.48
The only problem here is Tax in this case should be under total and be labelled (Of which VAT is otherwise it looks like you attempting to add the Tax/VAT on top.
If I change the customer to show prices ex VAT the displays changes to:
Sub Total: £3.48
Shipping: (ex vat) £0.00
Tax: £0.58
Total: £3.48
Nothing changes, the reason Sub Total is the same is because include VAT in sub total is true, in an ideal world this would change depending on the customer setting.
However is is not the major issue, as I said just turn sub total inc VAT to false and the sums all work. The problem happens when shipping is involved.
So again with VAT inclusive we see
Sub Total: £3.48
Shipping: (inc vat) (2-3 Working Days) £5.40
Tax: £1.48
Total: £8.88
Again if Tax was under Total this works just fine, however the problem now starts when I set show VAT to false for the customer
Sub Total: £4.38
Shipping: (ex vat) (2-3 Working Days) £4.50
Tax: £1.48
Total: £8.88
Now that, for a customer, might just be the most confusing thing on the planet. The Sub total has INCREASED. The reason for this is Sub Total is just shipping take away from Total. Now I have only one product added still.
In effect the customer sees the Sub Total as £4.38, yet in the basket all they have is £2.90 ex vat.
Granted this can only happen on a store with VAT and the customer viewing all prices ex VAT. However for the few that do, their total's will make no sense at all.
It may see a small problem but that confusing is enough alone to stop our ver 9.1 development and create a new control for the totals in an attempt to fix this.