round to the nearest 10th 3.899
The 8 is in the tenths place
You will use the next 9 for rounding
After that the digits have no relevance - I suggest you cross out the irrelevant digits so that you will get less confused.
so the question is the same as
round to the nearest 10th 3.89 (which is the same as round to 1 decimal place)
Now if the number in the next place (9 in this case) is smaller than five then you truncate
eg round to the nearest 10th 3.8 2 = 3.8
eg round to the nearest 10th 3.8 4 = 3.8
If the next number is 5 or bigger than 5 then the value goes up by 1
eg round to the nearest 100th 3.8 9 = 3.9
eg round to the nearest 100th 3.7 5= 3.8
If the last digit that you need to put up by 1 is 9 then you have to put the 2 last digits up, (with these ones you have to keep the zero after the point to show that you have rounded to 1 dec place)
round to the nearest 10th 5 3.96 = 54.0 (i think of it as 39 goes up to 40 BUT keep the decimal point in the same place)
round to the nearest 10th 5 3.99 = 54.0
If the last 2 digits that you need to put up are both 9 then you have to put the 2 last digits up,
round to the nearest 10th 8 59.95 = 860.0 ( i think of it as 599 goes up to 600)
round to the nearest 10th 79.95 = 80.0 ( i think of it as 799 goes up to 800)
and so on.
+118654 
