When rounding off, values from 5 to 9 are taken as 1 while values from 0 to 4 are taken as 0 .
When you round the value up or down , you add it to the next value. Remember it’s done from right to left
So, given 423.6059,
9 is taken as 1 and added to 5 which becomes 6. 6 also becomes 1 and added 0 which which becomes 1. 1 is 0 and added to 6. Finally, 6 becomes 1 and is added to 3 making it 4 .
So we are left with 424 which is now in 3 significant figures
