To do this, it will be easier to think of 757 as 0757. To round to the nearest 1,000 you first take only the numbers of place value 1,000 and greater. In this case, that's just 0. Then you look at the next digit on. If it's 5, 6, 7, 8 or 9, you round up. Otherwise, you leave the digit as it is. In this case, we have a 7, so round up, giving us 1.
That means that 757 rounded to the nearest 1,000 is 1,000.
757 rounded to the nearest hundreds place is 800
760
100
1000
1000
1000
176 rounded to the nearest 1000 is 0
1000
1000
1000
0
1000