The Mass Product Actions provides several variants for mass price updating. It is a replacement of the current price for chosen products, adding or subtracting from the current price and percentage of the current price.
Regardless of the chosen variant, the final updated price value is calculated with rounding to the second decimal number. For example, if the price is 10.274 - it will be rounded to 10.27, and for the price 10.275 it will be rounded to 10.28. If the price is 10, and it must be corrected as 1.156%, the result price will not be 0.1156, but it will be rounded to 0.12.
The Mass Product Actions does not let the user interface change the rounding parameters via the Magento backend admin panel.