The Big 5 ticket includes a 1-day hop-on, hop-off city tour as well as entry to WILD LIFE Sydney Zoo, SEA LIFE Sydney Aquarium, Madame Tussauds and Sydney Tower Eye. It costs $107 per adult.
A multi-attractions pass, which covers all 4 of these attractions, is $85 when bought online. This gives you a saving of $37. But that's only if you see all 4 attractions.
Attractions start from $24.80 per adult (based on the online price for Sydney Tower Eye) so you'd have to visit at least 2 in the day to make the cost worth it.