Hello Harry,
Well you cannot add Tax in Quote directly. You will have to input your Tax in Quote product Lines (tax for each Quote Product). And this can be done manually on every quote product.

Once you input the Tax in Quote Product, then the result will be appearing in the Quote as total sum of Quote Product Taxes.

You would be able to find Quote product Entity and have N:1 Relationship to Quote.
Hope this helps!
Regards, Abhishek Bakshi If you find this post helpful then please Vote as Helpful and Mark As Answer. Check my blog on https://mydynamicscrmblog.wordpress.com/