415 is already rounded to the nearest tenths place as well as to the units place.
400
478.5
400
420
15,549 to the nearest hundred
420
To round 415 to the nearest 10, we look at the digit in the tens place, which is 1. The digit to its right, 5, is greater than or equal to 5, so we round up. Therefore, 415 rounded to the nearest 10 is 420.
400
There are 25.4 millimetres in one inch. Therefore, rounded to two decimal places, 415 millimetres is equal to 415/25.4 = 16.34 inches.
Dividing distance travelled by speed gives 450/65 = 6.923076 recurring (that is, 6.923076923076...) hours or 415 minutes, rounded to the nearest minute.
420.
That would depend on what you were rounding it to. If rounding to the nearest whole number, then it does not need rounding. If rounding to the nearest ten, it would be 420. If rounding to the nearest hundred, it would be 400.