[feetsoup]

That's easy to say, but when it comes to shopping at the store, picking up several items and not actively thinking about it, are you really sure you aren't unconsciously interpreting that 9.99 differently from 10? Personally, I like to think that doesn't work on me, but at the same time I've caught myself saying something was '9 dollars' when I've been distracted and it was in fact 9.99.

And even if 9.99 really is 10 for you, it could mean that you're different than most people, rather than the methodology being faulty.

[johnisgood]

I found it odd that my girlfriend would say out the cents, because personally I have always been rounding up, and never considered the cents, for example.

[HocusLocus]

I try to keep two things in my head when filling a grocery cart, an accurate tally of dollars and a numberless sense of "where in the dollar the cents remainder is presently", like the position of a progress bar on a screen. I find a remembered visual progress bar does not distract me from the arithmetic, and when I spot one of those silly prices ending in .95 or .99 the bar resets to a tiny bit and I add a dollar. My mental progress bar generally jumps in approximate ~1/4 steps and when the total is accurate to within $2 with many items that is a win.