Someone please correct me, but taken that each operation causes up to one bit of error and that we perform 60e6 operations ...

We'll need calculate with 60.000.000 bits to be 100% sure of avoiding rounding errors.

So a brute force calculation should be ruled out.

Furthermore what is mathematical correct?

Though it's taught in school, any rounding that maps 0.5 to 1 is with 50% probability wrong.