Day Open price of Stock

Open price for TEXMOPIPES on Jun 27, 2016 is 28.9 if fetched daily. If we fetch it on 1 minute timeframe, it is 27.2. Is day open price different from 9:15 1 minute candle

What is the exact price on which first transaction happens for retail when day starts?

Suggest you to first read this answer on why not all ticks show up on charts. 

The  daily chart that you see is based on the end of day bhavcopy released by the exchange which mentions the exact open high low close of the day, based on all ticks that exchange received. This bhavcopy syncing for daily charts happen only by end of day. 

The 1 min chart OHLC is plotted from the data that is received on our servers. So the exact open for the day is what is shown on the daily chart.