It's not a big effect. As Mdragger showed, this adds less than 3ppm borates.
If you calculate for example the required acid addition to reduce pH from 8 to 7.6 for TA 80 without borates, but you actually have 3ppm borates in the water, then this acid addition will take you only to maybe 7.64 instead of 7.6. Most will probably not notice a thing, it's kind of in the tolerance you have for measuring acid amounts. And it's the safe way round, you'll always get less effect on pH by an acid addition.
The further down you go in pH, the less noticeable the borates become, for a pH-change from 7.5 to 7.2, you would hardly see any influence.
We also make some errors in calculating acid additions when ignoring that half of the TA may originate from CYA, which is actually quite a good buffer. This all creates a bit of noise, but luckily we are just talking about pools here, not lab experiments.
But I wouldn't add Borax to often, at some stage you should start considering borates in your acid dosage calculation.