<p>I'me looking for a function that would receive a time and would round it to the next/previous hour / half-hour / quarter / minute.</p>

Try this function
```
```
CREATE FUNCTION [dbo].[RoundTime] (@Time datetime, @RoundTo float)
RETURNS datetime
AS
BEGIN
   DECLARE @RoundedTime smalldatetime
   DECLARE @Multiplier float

   SET @Multiplier= 24.0/@RoundTo

   SET @RoundedTime= ROUND(CAST(CAST(CONVERT(varchar,@Time,121) AS datetime) AS float) * @Multiplier,0)/@Multiplier

   RETURN @RoundedTime
END

select dbo.roundtime('13:15',0.5)
```
```
The 1st param is the time to be rounded and the 2nd will be base on your list (0.5-half hour, 1-one hour, ...)