Lighter:
as for why prices seem to come out at $9.99, I'm guessing it is similar to the situation in the UK.
You'll often see prices ending in an odd 99p (or house prices in £XXX,999). In the case of houses it may be to make people think they're paying less than a given round sum, and the same was 9to some extent) true of shop prices (Oh, £8-99, that's not even Nine pounds!).

But that level of gullibility is no longer common.

One of the main reasons for the shop price of (for example) a shirt being £8.99 is that the purchaser, even if they have almost the right money (A five pound note & four one pound coins), will wait for their change. This means the shop worker has to ring the item into the till & give a receipt and one penny change. If the price was rounded to £9.00 the customer might put the right money down & walk out. Dishonest shopworkers then just avoid ringing up the purchase & pocket the cash.