I have never tried this but I suspect it's likely to be a bit horrid. You can convert your PPT to PDF just by exporting it in PowerPoint; you can then convert the PDF into an epub using one of many different tools you can find online.
The problem is that depending on the conversion method you're either going to end up with a bunch of flat image files, which Kindle doesn't handle particularly well, and which are unsearchable and unreflowable, or you're going to just get the text ripped from the presentation with none of the page design etc. Neither possibility is very reader-friendly.
Kindle and iPad will read PDFs but I don't think you can sell PDFs through Amazon or iBooks...?
You could probably find a way of converting your presentation into a fixed-format book for iBooks - iBooks Author tool would be the thing to use if you're not a CSS wizard. You could export each slide as an image and drop it into Author, perhaps? You'd only be able to sell it through Apple.
You could also find a way of converting it to fixed-format KF8 for use on Kindle Fire or Kindle apps. That's a separate conversion though and I dunno how to do that easily.
I don't think there's a simple way to do this, unfortunately. If you google "PPT to EPUB" you may find some software that can do this.
