A word for “the shelves of candies or mints next to the checkout desk of a supermarket”

This is probably too imprecise, but the hyphenated adjective "point-of-purchase" could be used with a noun (display, rack, etc), which would give you two words total, if you accept that the compound adjective is actually one word. And the adjective could be reduced to "POP." Ask someone in management at a grocery store, and maybe she'll reveal an exotic bit of grocery argot.

These are impulse goods or impulse items.

Impulse Goods

Retail items known for their unplanned purchases and, therefore, kept near the checkout counters, such as candy, chocolate, magazines, novelties, snacks.

[businessdictionary.com]

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.]

Not a direct answer to the question, in that it doesn't necessarily have to be at the checkout, but an "end cap" is a location in retail for promotional goods, on which the stock are generally rotated.

(Retail: Store fixtures and layout) An end cap is a rack or counter at the end of a store aisle used to display promotional or sale items.

I'm adding this answer because it's a useful retail term.

This marketing blog talks about checkout end caps:

An eye-tracking portion of the study found shoppers spend time looking at all areas of a checkout’s end cap

This is sometimes referred to as the guilt lane.

For example:

https://www.theguardian.com/lifeandstyle/shortcuts/2014/aug/27/supermarket-guilt-lanes-customers-health-aldi-tesco-sainsburys-marks-waitrose

You could put toilet plungers on the candyrack and they'd sell like "hotcakes".

Everyone understands what they entice you to do - most people refer to the racks by the checkout counters as the "candyrack" it doesn't matter what's on them - toilet plungers, razor blades, batteries....candy

This is known as a point-of-sale display (POS display)

The actual industry term is 'front end' or 'front end racks'. Anyone stocking product (whether a store employee, sales rep, or merchandiser) told to place products on the front end will know that the products go on the racks by the cash registers.