Thinking about what I actually do. . .
A near equal test of a float ought to be a fractional error based on
the current value of the float.
$x tested for between $a*(1.0 + $errorfraction) and $a*(1.0 - $errorfraction)
If you're dealing with propagation of errors during processing of
data the fractional error is usually the one that's important.
Finances might be different but floating dollars have their own set
of problems relating to representation of decimal fractions.
--> A fair tax is one that you pay but I don't <--