Write a Python function `cube_nums(nums)` that takes a list of integers `nums` as input and returns a new list containing the cubes of each integer in the input list.
#### Example Usage
```python [main.nopy]
print(cube_nums([1, 2, 3, 4, 5])) # Output: [1, 8, 27, 64, 125]
print(cube_nums([10, 20, 30])) # Output: [1000, 8000, 27000]
print(cube_nums([12, 15])) # Output: [1728, 3375]
```
#### Constraints
- The input list will only contain integers.
- The function should return a new list without modifying the original input list.