Hi Chiew Ngee Ho,
I would suspect that the splitting you describe has already occurred in the ERP system, rather than in GTS. To be sure, set a break-point near the beginning of Function Module /SAPSLL/CD_SDOC_R3, and check the number of item entries when saving a Billing Document.
Assuming the split is coming from the ERP system, you could check & correct the pricing in BAdI /SAPSLL/IFEX_SD0C_R3 to remove the rounding errors.
If you are sure that the splitting occurs in the GTS system, please let us know. Then we'll do more analysis...
Regards,
Dave