Nearest thousands means that we want 3 decimal places. To approximate a number to it we see the next decimal place. If it is greater than 5, we round up, if it is less than 5, we round it down.
If it is exactly 5, we round it so that the last digit is even.
In this case, we have 0.4275. We want 3 decimal places and the fouth is exactly 5, so we need to use the third rule. Since the third digit is 7, if we round down, we will still be at 7, which is odd, so we need to round up, so we becomes 8, and even digit.
So, the approximation is 0.428.