We can't work out the taxes you'd have to pay unless we know where you are going and which airlines are being used.
Taxes to enter/exit Australia are different to taxes to enter/exit Japan. Taxes when the RTW is ticketed by Qantas are different to when it is ticketed by CX. Taxes for using LHR are different then taxes for using CDG.

An LONE4 ticketed by QF travelling SYD-SIN-NRT-KIX-HKG-JFK-DFW-LAX-JFK-CDG-HKG-MEL-SYD will have different taxes to an AA ticketed LONE4 MEL-LAX-SFO-ORD-JFK-HEL-LHR-HKG-NRT-SYD-MEL.