Education ceas and tds rate

Hi

Three slab rates at 5%, 20%, 30% and they are used for finding tds rates. While edu cess is 4%

Eg. 5×4/100+5 and use the same formula for 20 and 30%

This gives new slab rates 5.2%, 20.8%, 31.2%

Why like that? Its used for calculating TDS on bonus and gratuity perhaps. If bonus is 100 and tds is 100x5.2%

What is the tds section for gratuity?

Txs