I am uploading data, and in column A it post the times like this:

01.31.06
02.00.06
02.31.08
03.00.05
03.31.06
04.00.23
04.31.15
05.00.11
05.31.12
06.00.07

I would like to insert code that would round each time DOWN to the
half hour and then remove the seconds.

01:30
02:00
02:30
03:00
03:30
04:00
04:30
05:00
05:30
06:00

any suggestions?
thanx