Once you figure this out it’s fairly straight forward but it took me quite some time to figure it out.
this specific request is heavily dependent on JavaScript.
using this file modules/AOS_Products_Quotes/line_items.js
copy this file into your custom folder
/custom/modules/AOS_Products_Quotes/line_items.js
look in that file for “VAT” and start modifying the javascript file.
What I have done is taken the current tax drop down and duplicated it with a slightly different name “vat_pst” in my case and then do the calculations based on the new dropdowns.
I looked for a php/mysql solution when the answer was to brush up on the JavaScript which from what i’ve seen in the developer videos is the direction that sugar is going in. ie more and more javascript.
Sorry I don’t have a specific answer but hopefully that helps.