When rounding numbers the rules are simple.

If you have a number that is odd like 3.0 to 3.4 then you round down to 3.0

If your odd number is 3.5 to 3.9, then you would round up to 4.0

If you have a even number like 4.0 to 4.5, then you would round down to 4.0

If your even number is 4.6 to 4.9 then you would round up to 5.0.

Examples:

3.45 is 3.4

3.35 is 3.4

4.4 is 4.0

4.5 is 4.0

4.55 is 4.6