Basically estimating is rounding, im going to futher explain this with an example. For example: If I wanted to round a number by it's nearest tenth such as 678 (*example) there are 70 tenths now when you are estimating when you are rounding to the nearest number if the number has a higher value then 5 you increase the number if it is lower than 5 you STAY the same.
now 678, since the number next to it is 8, 7 increases and everything else turns into zero. so 678 rounded to the nearest 10th is 680!
