In SQL, I have a `DATE` variable which I want to round to the next available half hour (i.e. xx:30). Note that this shouldn't just be to the *nearest* half hour.

Here are some examples:

```
Time                   Expected outcome
2012-03-26 11:25 AM    2012-03-26 11:30 AM
2012-03-26 11:45 AM    2012-03-26 12:30 PM

```

Is there a way to do this in SQL?