Krishna, you must understand that what i described to you is manual operations. Users have to worry about time when to post taxes and about amount of tax (either to calculate this amout using intruments i showed you or to calculate it themselves)
You have to create apropriate tax flow or correct one that exists in the system.
Then when user knows base amount upon which he can calculate tax amount - he uses SAP intruments (i showed you) or he can calculate amount with their own instruments.
Then in edit mode open FDR investment transaction and on "Other flow" tab enter tax flow.
Then post tax with TBB1 tr.
That's it.