Found this on https://coupons.nine.com.au/dell#voucher-235612. 15% off entire store unless already discounted (as far as I'm aware). Just used it to buy a monitor and had no issues.
Searched for other posts with this coupon and could only find https://www.ozbargain.com.au/node/520210 which is now expired. Code still works.
Only posted a couple of times so let me know if I'm not doing this right.
Edit: Read comments - excludes G Series - update 24/09/2020 now working for G Series
Edit 2: try stacking with EPP5 for additional 5% off (19.25% total)- thanks dogsrummy for posting this in comments and loki niflheim and nitinsukhija for confirming.
Edit 3: code is reportedly still working despite passing expiry date…
Edit 4: code not working for Ultrasharp monitors. Thanks Herre. Tested on an Inspiron laptop and code was still working, so it's likely still useful in some cases.
Edit 5: code working for G Series now. May not work for some products - see comments.
Edit 6: try stacking with BONUS7 for additional 7% off - thanks Royale with cheese
Edit 7: code still working on some items. Thanks zaido.