Casey’s General Stores Inc. is donating $10,000 to the American Red Cross to support disaster relief in the six-state area hammered by tornadoes Friday night and early Saturday, the Ankeny-based company announced. In addition, through Dec. 31, Casey’s will be collecting donations for the Red Cross at the cash registers of its convenience stores via the “round up” function. The company also is sending a semitrailer truck filled with bottled water to Mayfield, Ky., one of the hardest-hit towns. At least 90 people were killed in the storms.