I wouldn't quickly assume Walmart's strange pricing practices are psychological.
I know that Walmart uses advanced analytics for doing pricing and expectation of sales. So it could be possible that these odd cent items aren't for psychological purposes but instead for building accurate pricing models. I can only speculate though but this is what I do and I know that's why we like odd cent items. My company helps eCommerce shops with pricing.
While I don't have the study readily present, there was actually one done where 7th and 8th graders were shown a number of items with "odd prices" most notably "x.99" prices and were asked later on if they could recall the prices, the distribution were heavily weighted against odd pricing. Most of students recalled either the exact price or rounded up. Very few rounded down.
I know that Walmart uses advanced analytics for doing pricing and expectation of sales. So it could be possible that these odd cent items aren't for psychological purposes but instead for building accurate pricing models. I can only speculate though but this is what I do and I know that's why we like odd cent items. My company helps eCommerce shops with pricing.
Articles such as this on Wikipedia (http://en.wikipedia.org/wiki/Psychological_pricing#Historica...) can give you an idea about how much speculation there is in pricing.
While I don't have the study readily present, there was actually one done where 7th and 8th graders were shown a number of items with "odd prices" most notably "x.99" prices and were asked later on if they could recall the prices, the distribution were heavily weighted against odd pricing. Most of students recalled either the exact price or rounded up. Very few rounded down.