Zaokruhlenie:
HOUR(A1) + ROUND(A1/(15/1440),0)*(15/1440)
tento vzorec ti da nasledovne chovanie:
06:02 -> 06:00:00
06:07 -> 06:00:00
06:14 -> 06:15:00
06:16 -> 06:15:00
06:19 -> 06:15:00
06:22 -> 06:15:00
06:23 -> 06:30:00

alebo takto:
HOUR(A1) + ROUNDDOWN(A1/(15/1440),0)*(15/1440)
06:02 -> 06:00:00
06:07 -> 06:00:00
06:14 -> 06:00:00
06:16 -> 06:15:00
06:19 -> 06:15:00
06:22 -> 06:15:00
06:23 -> 06:15:00

alebo smerom nahor:
HOUR(A1) + ROUNDUP(A1/(15/1440),0)*(15/1440)
06:02 -> 06:15:00
06:07 -> 06:15:00
06:14 -> 06:15:00
06:16 -> 06:30:00
06:19 -> 06:30:00
06:22 -> 06:30:00
06:23 -> 06:30:00

ak dostanes v bunke desatinne cislo, ako napr. 6.260416667 musis naformatovat bunku aby hodnotu zobrazoval v casovom formate (pravym klik na bunku a vyber formatovanie bunky z menu a vyber Cas)
daj vediet, ako to dopadlo.

... prípadne pozri riešenia tu:
http://www.ms-news.net/f749/excel-zaokrouhleni-easu-pul-hodiny-6383327.html
http://www.ms-news.net/f748/excel-zaokrouhleni-easu-ve-formatu-desetineho-eisla-na-pul-hodiny-6322160.html

Díky moc, funguje to.