Floating point imprecision

[hardgeus]

OK, I have been programming in C++ for over 10 years now and I've never run into this problem...I've always known that floating point operations are somewhat "fuzzy", but I always assumed it would be down to a resolution that I never encounter...well, in a point of sale app I wrote using QT, I am finding that for purchases totaling over $13,000 I am getting imprecision down to 0.1 (I'm running into 5 cents off)

At first I thought I was crazy, but after doing tons and tons of printfs, it seems that something flaky is going on. I have a function called RoundMoney that does a floor and a couple of divisions to force the float value to two decimal places. What's odd is that when I echo the value with qDebug:

qDebug() << fValue

I get the result I'd expect (I think it's 13125.2) ...but when I use

printf("%.5f\n", fValue);

I am getting the values that are off by a nickel (13125.240 or something close...I don't have my debug output in front of me) Note that my arithmetic comparisons (greater than, less than) reflect the value reported by printf and NOT the qDebug output. If anything, the qDebug output is "wrong" because it doesn't agree with the actual if( x < y ) comparisons I'm making. Basically my code looks roughly like this:

if( fOwed > fPaid ) {
printf("%.3f owed, %.3f paid\n", fOwed, fPaid);
qDebug << fOwed << " owed " << fPaid << " paid";
}

And my output (roughly) is:
13125.240 owed, 13125.200 paid
13125.2 owed, 13125.2 paid

How does QT "know" to truncate that .04??

I am looking for one of two possible solutions:

1) Do whatever the hell it is that QT is doing internally to "know" that I earlier truncated my value and ignore the remaining "imprecise" floating point values

2) Use something besides floating point values and arithmetic. Trolltech seems to have thought of everything with QT, is there some sort of high level "decimal" or "money" class to deal with this?