RY (sister site of Look Fantastic) has 25% off NIOD products, that stacks with 30% cashback + 15% Westpac bonus cashback from Shopback today. It works out to be 58.75% off overall using Shopback + Westpac.
NIOD is the premium range from Deciem, who also make The Ordinary. Here are some recommendations from Gothamista
As far as I can tell, there are no restrictions for cashback for The Ordinary (unlike cashback terms for Look Fantastic), so assuming cashback tracks, you should get 45% cashback from the listed price using Westpac. Note however that RY's prices are sometimes slightly higher than The Ordinary's own website for some reason, but overall it should still work out to be better than waiting for Deciem's annual 23% off November sale.
To get the maximum cashback before the $20 cap sets in, make sure your total spend is $133.33 or lower.
Has anyone purchased from RY before? How was the experience?