The surcharge for card payments is generally the cost born by the merchant for subscribing to the routing system in order to accept payment, and the RBA says this cost can be passed onto consumers. With cash, I would have thought it doesn't really cost much, if anything, for a staff member to hold out their hand and accept cash in notes and coins. It is not the consumer's responsibility for what happens to those notes and coins once they have paid (i.e. transport to safe, transport to bank etc.) as that is the merchants choice to do that.
If a merchant charges a card payment surcharge, and wishes to also charge a surcharge for cash, it will come with the caveat that all their pricing needs to reflect these costs, if there is no way to avoid a surcharge, as this will be in breach of consumer law (e.g. a cafe cannot advertise on their menu a coffee priced at $5.00 and also require a surcharge on top of 1.5% irrespective of how they pay. The price of the coffee on the menu therefore needs to be $5.08)
