Tds on software purchased??

Please guide me that whether TDS is applicable on Purchase of Software (i.e. Tally ERP). As the Invoice bill of Tally Solutions is as under:

Software (Tally ERP) Cost = Rs.50000/-

Service Tax @ 12.36%=Rs.6180/-

Central Sales Tax @ 5% On (50000+6180) =Rs.2809/- 

Total = 58989/-

I also want to know why the CST charged on Service tax? Whether co. can charge the tax on tax?

Please reply soon as its urgent??

Thanks in advance..