Remove milliseconds from timestamp

[johnathan.chick]

I have cells that contain a time and date in decimal form. Specifically:
40838.44059
40838.44058

When I format the cell as date and time, it shows:

10/22/11 10:34
10/22/11 10:34

I believe that there are milliseconds attached to the time, even though I am not showing them. I need to filter my data such that there are no duplicates, but this cannot be done since even the timestamps in decimal form are not equivalent. When Excel does the comparison, it looks at the decimal value, not the formatted value and thus they are not the same.

Is there an easy way that I can modify the timestamp so that it does not include any milliseconds? What i've done so far is extract the hour and minute from the time stamp and then sort like that. But doing that then requires me to have several additional cells and do some =text parameters with lots of ':'s and '/'s to try and put it all together so that it looks like the above format. I would ultimately like to somehow remove the seconds so that the date and timestamp only have hh:mm and return it to a decimal format so I can format the cells as date/time. Any suggestions would be helpful.

[ChemistB]

Try = INT(A1*24*60)/(24*60)
Is that acceptable?