Right. JS math is fairly buggy - in this case the function will round only when given 9 thousandths. I have no guess as to why it even rounds, but it seems to be different per browser.

Try more edge cases, like 0.145 which should produce 0.15, but fails and returns 0.14 (I checked in Chrome concole).

For n = 0 code will return 8, but it should be 4.

Also as far as I see you do not need to keep all values, you need only previous two.

Result for n == 0 || n == 1 is wrong, it should be 4.

You also do not need Aggregate, you could calculate sum within for cycle.