For 485 Temporary Graduate visa, You need to have adequate Health insurance to apply and it is visa condition that you need to maintain it.
OSHC (Overseas Student health cover) is acceptable health insurance if you still hold student visa when you apply 485 visa. You can start your OVHC (Overseas Visitor Health Cover) for working visas after your OSHC finish. (You need to have OVHC either immediately after your OSHC ends or before IMMI make decision, whichever comes first.)
If you are eligible for Medicare, then Medicare is adequate health insurance. Please note that most temporary visa holders are not eligible for Medicare but some permanent visa application for ENS (Employer Nomination Scheme) or RSMS (Regional Sponsored Migration Scheme) etc, you might be eligible for Medicare.
For 485 visa, make sure you maintain adequate health insurance through out your visa periods.
Source: Department of Home Affairs adequate health insurance
Contact Storyoz if you need to plan ahead for 485 and permanent visa application.