Bud wrote:
round(3348.86*.1,2) = 334.89
round(3348.86*.03,2) = 100.47
when added together 334.89+100.47 = 435.36
yet round(3348.86*.13,2) = 435.35

This is a normal anomaly of rounding. It is one reason
why the IRS, for example, suggests rounding only the
result of a computation, not intermediate results.

You do not need Excel to understand what is happening.
Consider adding 1.4 + 2.4, round to an integer manually.
If you round 1.4 and 2.4 first, your sum is 1+2 = 3. If you
round only the result, your sum is 1.4 + 2.4 = 3.8, which
rounds to 4.

I beleive it is because 100.4658 is rounding to 100.47

Yes. Alternatively it is because 334.886 is rounded to
334.89.

when it should be 100.46.

Why do you believe that? No matter: your expectation is
simply incorrect.

I really need these numbers to add up. If this is possible
it would be great.

There is no solution where, in all cases, f(A+B) = f(A)+f(B),
where "f" is any of the operations like INT, CEILING, ROUND,
ROUNDUP or ROUNDDOWN. You need to accept that as
a mathematical fact.

To determine the right solution for you, you need to decide
what your goals are. If you want an accurate final result,
it might be best to round only the final computation. If you
want the Excel computation to match what you would do
manually based on intermediate values displayed in cells,
you might want to round each intermediate result, accepting
a small error in the final computation. (There is also an
option to force this behavior for all spreadsheet compuations.
See Tools Options Calculation Precision As Displayed.)

Moreover, you might use ROUNDUP or ROUNDDOWN to
maximize or minimize the error in the final computation in a
particular direction. The choice is a tricky judgment call that
requires a detailed understanding of the purpose of your
computations.