If the cells values listed (i.e. C17 and H17) are functions of other numbers
(i.e. C17 is actually "=SUM(C15:C16)") and the formatting of these cell
display a numerical value of only 2 decimal places the function will still
use the unrounded numbers.

Example
C15 = "4.862"
C16 = "100.00"
C17 = "SUM(C15:C16)"

If the above was True the Sun of the fields is 104.862
However if the formatting for C17 was set for only 2 decimal places if will
display 104.86 as you have provided below.
Now if you use the C17 Cell in an equation as you are it will still use the
104.862, there for throwing the math off to not use the exact value.

The formula is working fine. You're experiencing problems with numbers.
Computers generally store numbers as floating point in binary, base 2 which
are approximations of decimal numbers, base 10. Some numbers in decimal can
be represented exactly in binary and others cannot. There are many articles
concerning floating point. Google IEEE floating point.
You can address your problem by rounding the numbers or computing the
difference as less than something like 0.000000001 to determine equality
Modern computers don't work in decimal. Older ones did and did not have this
problem. Progress, I guess.

Tyro