No, they don't do a calculation to add a VAT cost. They do a calculation to let you know how much of the 5.99$ is in fact the included VAT, and like i said, on receipts they have to let you know how much VAT they're charging.
The only thing you can point out is that they don't show the price without VAT on the receipt, but that's a bit irrelevant if you ask me. You know how much you're paying, and you know how much of that ammount is VAT.

What Korell is saying is that GOG are calculating VAT as 15% of $5.99, when in fact $5.99 is equal to the 'original price before tax' plus 15% of the 'original price before tax'. This means $5.99 is actually 115% of the 'original pricebefore tax'.
Value Added Tax is added on top of the price not taken from it. Therefore, the VAT value of 15% which makes up a part of the total price of $5.99 should equal $0.78 with the 'original price' coming to $5.21. Basically, GOG's assertion that $0.90 of every $5.99 paid goes towards to tax here in the UK is incorrect and Korell is right that the figure should be $0.78.
Interestingly if VAT is calculated at the old UK value of 17.5% and the calculation is rounded to the nearest cent at each stage than $0.90 would actually be correct. Perhaps they just didn't update the actual monetary value of VAT when they changed the percentage to the new rate last December.

More likely as VAT varies from country to country and can change from year to year GOG decided to go with 17.5% for everyone. Some end up paying a few cent more and some a few cent less. At the end of the day the final amout for everyone is still $5.99

Very true that could certainly be it.
Hell only knows what rate VAT is going to end up over here when the government realises it actually has to pay off the ridiculous mountains of debt it is getting us into.

If that was the point korell was trying to make then i appologize cause i didn't understand.
But in any case that would only work assuming that they're charging VAT at 15%. Since the % of VAT is not known, i don't know if it's 15%. VAT here in Portugal is 20% or 21%, for instance, so Delixe is right when he says that the VAT % doesn't reflect the actual % of VAT in every country, but rather a fixed % that more or less suits everybody.

I am not assuming they are charging VAT at 15%, as far as I understand it they must do so under UK law in order to sell me a product.
They state that percentage themselves both in the confirmation e-mails and at checkout (see attached image). All Korell pointed out was that the value they state as VAT does not correspond with the rate they stipulate.
There is a pretty good guide to VAT here. Although it applies directly to the UK, the principle should be much the same elsewhere.

Yep, you're right. The VAT is 15%.
And there is a small difference between the VAT in $ they display on the receipt and the actual 15% of VAT in $, so korell is right about that one aswell.
My bad guys. Feel free to post the facepalm pics now. This round is on me.

No worries, this discussion has actually been quite thought provoking and has raised a few things I have never really thought about with regards to companies like GOG who operate from one location but are potentially serving customers from anywhere in the world. I imagine it must be a logistical nightmare, especially with regards to legal issues.

Yes, the legal logistics must be a PITA. I'm guessing the guys who are in charge of playi...*ahem*...'testing' the games are the ones who with the really fun jobs.

I love that site. :)

Re: the VAT, GOG aren't actually charging you any tax, they are just trying to make it look like they are so they don't have to charge you =)
That's the only good thing about where I live, we have no tax for online purchases made outside of the country, thus we are charged $5.99/$9.99. Which is the same price as you.

Game testing is a lot harder than you'd think!
It's easier at GOG I'm sure, but at publishers, it's a very taxing task. Long hours and tedious play methods.

No doubt. But i'm sure they manage to squeeze in a little time for plain ol' fun anyway :)

If you know the name of the currency (or the symbol) you can also use Google. :)