When you specify ROUND=, PROC UNIVARIATE rounds a variable by using the rounding unit to divide the number line into intervals with midpoints of the form , where is the nonnegative rounding unit and is an integer. The interval width is . Any variable value that falls in an interval is rounded to the midpoint of that interval. A variable value that is midway between two midpoints, and is therefore on the boundary of two intervals, rounds to the even midpoint. Even midpoints occur when is an even integer .
When ROUND=1 and the analysis variable values are between 2.5 and 2.5, the intervals are as follows:
Table 4.27: Intervals for Rounding When ROUND=1

Interval 
Midpoint 
Left endpt rounds to 
Right endpt rounds to 

2 
[2.5, 1.5] 
2 
2 
2 
1 
[1.5, 0.5] 
1 
2 
0 
0 
[0.5, 0.5] 
0 
0 
0 
1 
[0.5, 1.5] 
1 
0 
2 
2 
[1.5, 2.5] 
2 
2 
2 
When ROUND=0.5 and the analysis variable values are between 1.25 and 1.25, the intervals are as follows:
Table 4.28: Intervals for Rounding When ROUND=0.5

Interval 
Midpoint 
Left endpt rounds to 
Right endpt rounds to 

2 
[1.25, 0.75] 
1.0 
1 
1 
1 
[0.75, 0.25] 
0.5 
1 
0 
0 
[0.25, 0.25] 
0.0 
0 
0 
1 
[0.25, 0.75] 
0.5 
0 
1 
2 
[0.75, 1.25] 
1.0 
1 
1 
As the rounding unit increases, the interval width also increases. This reduces the number of unique values and decreases the amount of memory that PROC UNIVARIATE needs.