I have to set up a tax called "Tax 17.5 "

It consists of 3 children taxes

'Getfund 2.5' = 2.5% of base amount

'Nhil Levy 2.5' = 2.5% of base amount

'VAT 12.5' = 12.5 of (base amount + (getfund2.5 + nhillevy2.5))

Sample Calculation:

base = 6589

getfund2.5 = 2.5% of 6589 = 164.73

nhillevy2.5 =  2.5% of 6589 = 164.73

vat12.5 = 12.5% of (6589 +(164.73+164.73))
              = 12.5% of (6589 + 329.46)

               =12.5% of 6918.46

               =864.81

Total Tax(17.5) = getfund2.5 + nhillevy2.5 + vat12.5

                 = 164.73 +164.73 + 864.81

                 =1194.27

How can I achieve this?