How can I find the nearest 15 (or 10) minute interval in python ?
e.g.

```
>>> datetime.datetime.now()
datetime.datetime(2011, 2, 22, 15, 43, 18, 424873)

```

I'd like the current 15 minute interval (15:30-15:44) so I'd like to transform the above datetime to a 

```
datetime.datetime(2011, 2, 22, 15, 30, 00, 00)

```