5596.27+1157.85+559.63=7313.74....
I've readjusted the rounding and it still comes out the wrong answer.
Is the "weird part" that it summed to 7313.74 instead of 7313.75?
If so, then the problem might be that your columns are using "single precision" floating point numbers [32-bits], and if you could change the type of the values to "double precision" floating point numbers, then you might get better [i.e. less noticeable] rounding error.
[Note that there will ALWAYS be rounding error when working with floating point numbers - the only question is HOW BAD the rounding error will be.]
Beyond that, there are some known bugs with the mathematics package in Excel 2007:
Excel 2007 Multiplication Bug
Monday September 24, 2007
http://it.slashdot.org/article.pl?sid=07/09/24/2339203
Modifying the multiplication equations as below can eliminate the hidden stuff and solve the penny problem:
L14=0.01*INT(100*L12*0.29+0.5)
L15=0.01*INT(100*L12*0.06+0.5)
etc.