In the "Creating Quick Monster Stats" section of the DMG (p.274) we are given the procedure for determining the CR of a new DM-designed monster. Step 4 of that procedure (pp.274-275) tells us to calculate a defensive challenge rating, an offensive challenge rating, and then the
Average Challenge Rating. The monster's final challenge rating is the average of its defensive and offensive challenge ratings. Round the average up or down to the nearest challenge rating to determine your monster's final challenge rating. For example, if the creature's defensive challenge rating is 2 and its offensive rating is 3, its final rating is 3.
How are we to take the instruction to "round up or down"?
Does the DMG mean to say that it is DM's choice (rather than defined procedure) whether to round up or down? And that once that decision is made you move to the nearer CR in that direction?
Or, is this passage saying that the rounding should take you to the nearest CR, regardless of whether this means rounding up or down? For example, if the DCR was 1/2 and the OCR was 2, the average CR would be 1.25, which we would round down to 1, because 1.25 is nearer to 1 than 2. But if the DCR was 3 and the OCR was 1/4, the average CR would be 1.625, and we would round up to 2 because 1.625 is nearer 2 than it is 1.
The example then given shows rounding up, but in the confusing case of 2.5 being equidistant from both 2 and 3, which doesn't let us parse which of the two possible meanings is intended.
There are a number of CR-calculation questions on this site, but I haven't found this specific question. I understand that the final CR is by DM fiat, involves many other considerations, and is not a direct result of this specific procedure - I am just trying to understand what the actual procedure described in this passage is.