rounding timestamp

Hello

I need to output a timestamp attribute formatted to fixed-width, no spaces
nor separators, something like

test=> select to_char(timestamp '2003-10-24 15:30:59.999',
'YYYYMMDDHH24MISS');
to_char
----------------
20031024153059
(1 row)

But my problem is that to_char truncates the fractional seconds, and I need
to round the value to the nearest integer second. In the above, I would need
the output rounded to 15:31:00, which is just a millisecond away, for
example. But I couldn't find a function to round a timestamp. Are there any
workaround?

thanks
cl.