When are exact numerical results required?

Test case for TAN() currently is:

=TAN(PI()/4.0)

with an expected result of:

1±ε

However a test case for LOG() is:

=LOG(8*8*8; 8)

with expected result of 3 (with no epsilon).

Is this intentional? I suspect that few implementations are going to be optimized to produce exact results here.

Do we have a general rule here? Shouldn't it be that any function that has a domain of real numbers should be allowed an epsilon on test results? And only functions whose domain consists of the integers should be required to give exact results?