When you [url=https://hotcakescommerce.zendesk.com/hc/en-us/articles/208992646-Settings-Taxes]enable VAT[/url], products will already have VAT included before adding the product to the cart. Are you trying to show the VAT breakdown prior to checkout?

Yes, when you add something to the cart it shows:
[img=https://www.bondforwebsolutions.nl/images/hc/1.png]1[/img]

So the product is 99, the total is 99 and the total ex vat is 99

Then I click on Payment. It will show:
[img=https://www.bondforwebsolutions.nl/images/hc/2.png]2[/img]

So the product is still 99, but the total changed to 119,79 incl. vat

Then I go back to the cart and now it will show:
[img]https://www.bondforwebsolutions.nl/images/hc/3.png[/img]

So the product is 99,- the total is 119,79 and the total ex vat is still 99,-

This is a total show stopper, vat should always be shown so, in the 1st image, it should look like the 3rd image.
Otherwise we can't use this...

Please excuse in ignorance on my part, since I don't know VAT as well as I'd like. I also have not personally been keeping up with VAT over the past two years. I may ask a lot of questions and I'll need your help if there is anything to "fix." :)

In your example, which value is the correct value? Sometimes it really helps to have a tabular example provided for me to really "get it."

Is this a specific requirement for the country/countries you're trying to support and sell in? Do you know if there are other countries who may recently have incurred different rules/requirements for the display and calculation of VAT?

Well, besides the fact that it might be a requirement.
Don't you think that it is strange, or at least does not give a customer a lot of trust when at one point he sees a total of 99 euro and then when he comes back, he sees a total of 119,79.
I mean the total should be the total...