HI
I think, Please check in OBY6 ,Here check the check mark of Tax Base is net value,Whether it is ticket or not!
If it is not tick,
system will calculate like below:
For example: 1000 Tax amount will be: 1000*8/108=74
If it is ticket, System will calculate like below:
For example: 1000 Tax amount will be: 1000*8/100=80
Based on the system will behave .
Regards
asuvamsi