I don't think the Hindu population have a set "holy day" in the same way that Christians mark Sunday, Muslims Friday, Jews Saturday - but I am prepared to be told that I am wrong.
Yes, agree with society and 23 that followers of the many religions would stop to celebrate their own holy days, but in my understanding India doesn't have any one rest day. They keep weekends these days but like us, the world is generally a 24-7 society these days.
In case you simply wanted to know whether their working weeks are separated by fixed days off then, yes, Sunday is generally a day when people do not attend work (part of the employment law) and usually half of Saturday as well, although that applies in particular to government employees and offices that do not deal with customers. Shops are usually open pretty much all of Saturday but Sunday is a case of shops mostly closed.
karl shops are not closed in India on sundays. Shops are never closed in India! (apart from unforeseen circumstances such as when a family member of the shop owner dies in which case they can be closed for anything up to 10 days out of respect)
my sister in law lives in Bangalore and works for the Kingfisher group, she has Sat aft and Sundays off, same in Goa where most Goan born people are RC and attend church at least once on Sundays.