To the nearest thousandth is another way of saying to three decimal places. It is usual to apply 5/4 rounding, i.e. if the fourth decimal place is below 5 it is just discarded, if it is 5 or above value of the third decimal place is increased by one.
Thus 5.916079783 to the nearest thousandth is 5.916.
It is 6.981 when rounded to the nearest thousandth
88.564
0.370
174.689
8.246
8.924
It is 6.981 when rounded to the nearest thousandth
34921.000
88.564
70.659
0.370
145 is rounded to the nearest ones. 145 rounded to the nearest thousandth is 145.000
800.130
174.689
8.246
287.287
32.346