According to a press release issued by the ICC, match referee Ranjan Madugalle imposed the fines after Dhoni's side was ruled to be three overs short of its target at the end of the match when time allowances were taken into consideration.
In accordance with ICC Code of Conduct for Players and Player Support Personnel regulations governing minor over-rate offences, players are fined 10 per cent of their match fees for every over their side fails to bowl in the allotted time, with the captain fined double that amount.
If Dhoni is found guilty of one more minor over-rate offence in Tests over the next 12 months, he will receive a one-match suspension as per the provisions of the ICC Code of Conduct for Players and Player Support Personnel.
The offence is contrary to Article 2.5.1 of the code which relates to minor over-rate offences. The penalty was accepted by India without contest so there was no need for a hearing.