Is it needed. Because with the detector block you detect those numbers and then a trade is created. But this trade could be opened at a little bit different price, not at exactly the round number. If the trade is off with let's say 2 pips and you set SL and TP at round numbers, one of them will be 2 pips bigger than the other.
Otherwise it can be calculated. As you can see, what we do with that formula is to remove the last parts of a number. if we have 1.2345 we can remove the last 5, last 45, last 345... But it also depends, because what if we have 1.2678 - should we use MathFloor or MathCeil? Should the rounded number be 1.26 or 1.27?