What is the rounding logic is for invoice total calculations?

What is the rounding logic is for invoice total calculations?

Hello,

So I know Books has the option of either rounding to whole numbers or rounding to 2 decimal places. I prefer the 2 decimal places option, but I'm trying to understand what is the logic for that. 

For instance, if the calculation has a an absolute result of 1.88888. To make it two decimal places, does it trim after two decimal places to make it 1.88 or round to 2 decimal places to make it 1.89?

Cheers,

Sid