How can we improve WHMCS?

I would like to see tax calculated per invoice line and not on the total.
Why?

2 resons
1.) If you deliver services that have 2 seperate tax rules you dont need 2 invoices.

2.) Most accounting programs and our dutch law state that you need to pay tax for every product you deliver and not on the total.

let me explain where things go wrong:
the errors appear when things are rounded and calculated.

say i have 3 invoice lines

item 1 price 3.99 exclusive vat
item 2 price 4.99 exclusive vat
item 3 price 5.99 exclusive vat
whmcs sums the exclusive tax price 3.99 + 4.99 + 5.99 = 11.97 exclusive vat
say we have 21% tax then the total = 14.97 + 3.14(rounded from 3.14369) = 18.11

so the total that is being invoiced is 18,11

the dutch law and most accounting calculate like this

item 1 price 3.99 exclusive tax
the vat is calculated 3.99 21% = 0.84 (rounded from 0.8379) total for this item = 4.83

item price ex vat total
item1 3.99 0.84 4.83
item2 4.99 1.05 6.04
item 3 5.99 1.26 7.25
--------- --------- -------
14.97 3.15 18.12

And the total being invoiced here is 18.12

the organisation that controls the tax expect us to calculate by the 2nd way

So i love to see a way this can be fixed.