[BPCS-BIL] Rounding at Sales Invoice Amount

Hi All,
 Would you like to share your experience about rounding at Sales Invoice ?
Is it true that BPCS round amount net price and tax at invoice line level, 
not at total invoice level ..or maybe I don't setup parameter incorrectly?

Example:

*(Setting)*
Round Type: Half adjustment
Round to position type : 1 
Tax Rate: 10%

I have 1 invoice with 3 inv line. All of these inv lines have same setting 
above.

*(SIL.ILNET )*
SUM(97.5 + 97.6 + 97.8) for invoice #1 = 292.8
After rounding, it should be 239

*(SIL.ILTA01)*
SUM(9.75+9.76+9.77) for invoice no. #1 = 29.29
After rounding, it should be 29

But.. what I found at SIH.SITOT and SIH.SITAX ?
SITOT = 324 and SITAX = 30 

I assumed that 324 was origined from 294 + 30 (sitax).
294 = half adj(97.5) + half adj(97.6) + half adj(97.7)
30 = half adj(9.75 ) + half adj(9.76) + half adj(9.77)
 Thanks in advance..