I am looking for a simple point and shoot camera with a macro function to be able to take photographs for eBay auctions.
Are there any P&S cameras with this function?
There are plenty. What I recommend though is a compact with manual controls and for the purpose of eBay, unless you are selling truly miniature items such as insects, they are more recommended than DSLRs and SLDs.
A number of ultra-zooms are actually capable of extremely close focusing distance, as close as 0cm even! Although you will have lighting problems if you get that close, any of those models will do to focus closely. Not only that, the depth-of-field will be much greater than with an interchangeable lens, which is less artistic but arguably better for selling products.
The Canon Powershot SX150 (1cm min) or older SX200 (0cm min) are great choice in a compact form-factor. You can also go with an ultra-zoom like the Canon SX40 or Fuji HS20 EXR. Since these cameras have manual controls, you can set the aperture very small to capture an large depth-of-field. Just make sure to keep the ISO low for getting quality output and using a tripod for stability.
Not in the literal sense, no -- but almost all of them will let you take close-ups that look a lot like macros.
The thing about point-and-shoots is that they use very small sensors (typically around 4.5x6mm). True macro shooting means subject magnifications of around 1:1 on the film or sensor, so a point-and-shoot that actually did macro would allow you to fill the frame with a 4x6mm subject.
I have a bottom-of-the-line Canon Powershot A490 for rough-and-tumble (it has a 1/2.3" sensor, which is 6.16mm by 4.62mm). It doesn't shoot true macro, but it will let me fill the frame entirely with a subject that is 1.5" by 2" at maximum optical zoom at its closest focusing distance. On the camera's sensor, that's less than 1/8 life size, so it's nowhere near macro in the technical sense. Getting the lens to focus that closely is no mechanical or optical feat. But if the same shot were taken on a full-frame DSLR, it would be about 70% of life size, which is definitely in macro territory. (Okay, it would be a whole lot better picture too, but that's outside the scope of the question.)
So with just about every P&S camera out there having an extreme close-up function thanks to their small sensors, and with plenty of pixels to crop from for a resolution sufficient for eBay and the like, your choices are pretty much wide open. And keep in mind that although better cameras with larger sensors might not be able to focus quite as closely, you get the ability crop from a higher-quality image (sharper and less noisy) if you have to.
While Stan is technically right about what macro really means, I'm interpreting your question as looking for a point and shoot that can go down to a small field of view so that you can take detailed pictures of small things.
I looked for exactly that a few years ago to upgrade our "office" camera. We design electronics and circuit boards, so occasionally we have to send pictures of small things to remote customers or suppliers. This was probably around 5 years ago, but I ended up picking the Fuji Finepix F20 (from memory, may not be the exact name). Surely things have changed by now, but at the time Fuji seemed to be paying more attention to closeup detail capability than the others in the point and shoot realm.
The F20 has its annoyances, but it works well enough for the purpose. Like most point and shoots, you can't really control aperture. You can't, for example, chose a fixed small aperture to get good depth of field since you know the camera is on a tripod and you don't care how long the exposure is. It has these stupid and totally unintuitive program modes like "party", "museum", "on side of road with flat tire", and whatnot. Still, you can give it enough hints to be useable. Here is a example shrunk from a 1200 x 900 section out of the middle of a 2848x2136 frame:
It's not a great picture, but it says "fix your manufacturing process to stop leaving junk on my boards and get a sighted person to do inspections next time" well enough.