I would go with "impulse display shelf".
Google for it and see the resultant images.
(Googling for "candy rack" as suggested by Silenus in comments returns relevant images too; however you want a term to describe the ones specifically found near checkout desks which can and do hold things other than candies like mints, chewing gums and other usually small "impulse purchase" items).
I am not into retail; however, I know why exactly these are placed near checkout desks - to encash the temptation (and consequent impulse) that shoppers feel to just chuck in a couple of those (usually low-value) items into their shopping basket.
[Edit: I realised that dangph already gave a close answer to mine. I did not realise that before posting my answer.]