Talking about iit/nit these colleges are under the central government and do offer a fee waiver for sc candidates and the whole tution fee is waived off for sc candidates but they have to pay other fee like hostel ,mess etc but on the other hand iiits may be private or be made on ppp model and here there is no concession for sc candidates and they have to pay the fee as given by the institute for more info you may visit the website of concerned institute.