You need to create this route on your package, after clicking on this, action will perform and user will redirect here (https://prnt.sc/olc5mx - this is for paypal) then will redirect for payment (https://prnt.sc/olc7io - paypal screenshot).
Right Now tax is depends on country, state and zip (In case of all - *), so when you add product in cart or update it, tax can not update as it don't have any of these fields and during time of checkout it gets these fields so its get updated there.
If you want to change it & want it to work beyond country, state and zip, then you can request for customisation.
i only mentioned it as a improvement for Bagisto.
I wasn't sure if I had to report it on the forum or on the Github issues page.
I could add the fields myself and create a pull request on Github, but only if you confirm that it would be an added value for the platform, so that I don't waste my time on functions that won't be merged