In the invoice, we can selected the way to post as a separated Invoice. However, the total price is changed by a round with the calculated tax.

e.g. (price =113.95, sold tax=17%)

Quanty     total price (no tax)                      total price (included tax)

296       28828.38   (<28828.376)               33729.200    >      33729.20

15         1460.90      (< 1460.897)               1709.249     >         1709.25

                                                                                         (Sum 35438.45)

<not separated> 

311       30289.28     (< 30289.274)             35438.458     >      35438.46

296+15 > 35438.45

311 > 35438.46

0.01 difference

The calucutating of including tax should be done after sum total price.