-3dB on filters, just approximated?
You are not mistaken, it is 3.01 dB

20log\$_{10}(\dfrac{1}{\sqrt2})\$ = -3.01029995664 !

As a percentage to a voltage ratio, the 0.0103 dB is 0.1186% so not entirely dismissible.

If you were talking about the signal to quantizing-noise ratio of a 24-bit ADC, the error you'd get for using 6 dB (as opposed to 6.02 dB) would be about 0.5 dB. That's an example when the more precise number is used.