I've never figured this out in all of the 6 years I've been in New Zealand. This is the latest in the craziness of pricing in supermarkets.
In the UK, if you bought more of something it would cost less per item. New Zealand has a different take on this. In a hell of a lot of cases, if you buy more of something, it actually costs proportionately more! I've seen this happen on cereal quite a lot such that the larger box is pro-rata more expensive than the smaller one.
I saw another example of this earlier today. A sachet of cat food is 59c. A box of 6 sachets is $4.03! Not just a little over $3 which you might expect but 49c more than six individual sachets! But wait, it gets worse. A box of 12 sachets is not a little under twice the price of the box of six but actually $8.10! Which is not only worse than buying two boxes of six but even worse still than buying a load of singles.
This makes no sense to me. Can anyone please explain to me the logic here? The only thing I can come up with in the case of the cat food is that the extra box around the sachets mean more manufacturing cost. However, this wouldn't be the case with cereal.
Of course, the other alternative is that people in general don't check which size is cheaper. If that is the case then that's very bad since it's forcing all of us to pay over the odds for larger items.