T&Cs here. Enjoy :)
*All items listed in the following categories are excluded: Cars, Bikes, Boats (9800), Car & Truck Parts (6030), Coins (11116), Collectables (1), Gift Cards (184609), Other Lots More Items (88433), Real Estate (10542), Services (316), Tickets, Travel (11730). And all items sold by the following sellers are excluded: Bunnings Warehouse, Fantastic Furniture, Coles Supermarkets, Officeworks, Target.
Many conflicting responses from eBay customer service reps in the comments below. Some have successfully gained $5 vouchers, others have been told it's a targeted promo. Hopefully eBay will adjust the T&Cs to clarify the status of this code.