Round to the Nearest Half

[math]::Round($number * 2, [MidpointRounding]::AwayFromZero) / 2
Details
Round a number to the nearest half (.5).

Example
PS C:\> $number = 3.64285714285714
>> [math]::Round($number * 2, [MidpointRounding]::AwayFromZero) / 2

3.5