Maybe it depends on the software you are using - if I have a 15-minute (or whatever) bar/candle chart running on live prices on the charting software I use the final bar/candle (on the right edge of the chart) does update very tick. So while the bar is forming the 'close' price is changing (running up and down the bar/candle, or extending the bar/candle) as new ticks come through, until the 15 minutes (or whatever) is complete then the last price tick in that 15 minutes (again, or whatever period) is the final 'close' price and then a new bar/candle starts to form.