[Boost-users] boost::posix_time::time_period - how to round seconds?

I am building intervals using 0.5h increments (1800sec) in a cycle. The interval length is 1800sec also 8:30 am is used as start date. last of my interval looks like this: [2009-Apr-07 14:30:00/2009-Apr-07 14:59:59.999999] because of this weired endpoint my data with the timestamp of Apr-07 15:00:0000 does not fit into the interval How can I fix the interval to be [2009-Apr-07 14:30:00/2009-Apr-07 15:00:000000] ? Thanks