40
37 rounded to the nearest 10 is 40.
21 over 40 rounded to the nearest fourth is 0.5
The answer is $39. If the cents are 50 or over round up to $40 dollars, but because it is only 49 cents the number is closer to $39 so round down to $39.
40
If you are talking about 40 dollars, the answer is 40. It can't be 39 or 41.
40
40
40
40
40
40
40
40
40
40
37 rounded to the nearest 10 is 40.