Bundlestars has it included in their € price,
Humble just doesn't collect it (us based),
Groupees deducts it from the $ price without the user noticing or paying more.
IG adds it on top on payment

And we call it ÁFA. But VAT is the generally accepted global term.
Bundle Stars and Humble integrate it in the normal price and pay the VAT themselves. IndieGala and a good number of other sites decided to add the VAT on top since they apparently have a much smaller profit margin due to the happy hour deals.

So the happy hour is kind of confusing. If you bought the bundle (NOT as a gift) during the first week it was available, and bought the top tier (if it was available in tiers), then you will get 4 bundles for the price of 1 during happy hour. If you did NOT buy the bundle during the first week, you will get 2 bundles for the price of 1 during happy hour. You MUST check the "Yes. Buy as a gift" box when buying during happy hour or else you don't get this special deal.

So, for this bundle if you pay the $4.99 during happy hour you will get either 2 or 4 bundles depending on whether you bought it previously. The gift bundles show up in your IG account under the normal bundle. You can either give away the entire bundle or click into it and gift/reveal the individual keys.

You can also pay more, according to the chart at the "check our gift packs" section of the bundle page, you can get even more copies:

Get 2 bundle gifts paying more than: $9.78
Get 3 bundle gifts paying more than: $13.92
Get 4 bundle gifts paying more than: $17.56
Get 5 bundle gifts paying more than: $21.21

This is also a bit confusing, because in happy hour each gift is multiplied, so, assuming you bought the bundle normally in the beginning, each "bundle" in that list is actually 4 bundles. So pay $9.78 to get 8 bundles, or up to $21.21 to get 20 bundles :) And you can do that twice, bringing the total up to 40 bundles. This is the limit that IG allows.