Ithaca wrote...
....
The specification varies from a whole number to a decimal, depending on the
sample tested. *If the spec is 5 then what I'm actually using in the equation
is 5.49 such that, when rounded to the correct level of precision, the result
is "not more than" then given spec. *If the spec is 0.2 then the value in the
equation would be 0.249.

So comparisons at 1 significant digit?

The problem is that I'd like to make this one spreadsheet work for all
samples and therefore all specifications (5 to 0.2) and the quick formulas I
know of won't work for something that changes the level of precision.
....

For comparisons at 1 significant digit, try

=IF(TEXT(A1,".0E+000")<=TEXT(S1,".0E+000"),A1,"Fai l")