Note that there are lots to be considered. For an Australia-USA trip, these will be included:
Fuel Surcharge. This depends on the number of sectors. So if just SYD-LAX-SYD on QF, it will be $60 per sector or $120. If you have connecting domestic sectors then it will be more.
Aus Departure Tax. This is also calls the Passenger Movement Charge and is $38 per passenger.
Noise Levy. If you have an arrival into SYD then you will have to pay $3.40.
Passenger Serivce Charge. This varies by airport. For Sydney it is $20.58 for each departure and arrival, making a return trip $41.16. And other connecting domestic sectors will also incure these charges.
In the USA there are lots of small fees that add together to make a significant tax/levy amount. Again it depends on how many and which airports you pass through.
USA Federal Security Tax = US$2.50 (A$3.30) per airport (max of 4) so toal of A$13.20.
USA International Arrival Tax = US$13.40 (A$17.60)
USA Customs = US$3.00 (A$3.90). Also called "Animal and plant health inspection fee).
USA Immigration Inspection Fee = US$6.00 (A$7.90)
USA Arrival Customs Fee = US$5.00 (A$6.60)
Various USA Airport Passneger Movement Fees depend on the airports used.
You are quite entitled to ask the travel agent for a breakdown of the fees.