Mumbai, Aug. 19 -- The Indian rupee extends previous day gains in opening trades on Tuesday to a three-week high. INR commenced at Rs 87.24 per dollar and climbed to a high of 87.20 so far during the day. Yesterday, rupee appreciated 23 paise to close at 87.36 against the US dollar, supported by strong domestic equities. Indian shares rose sharply on Monday after Prime Minister Narendra Modi unveiled plans of the biggest tax overhaul since 2017 over the weekend, boosting stocks across sectors like auto, financial, real estate, consumer and cement. With robust GST collections and a broad tax base, government sources indicated that nearly 90 percent of the items in the 28 percent slab will now move to 18 percent. S&P upgraded India's rating...