From http://stackoverflow.com/questions/7797693/force-uitableview-to-scroll-to-tops-of-cells

UITableView+ScrollToCell

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate(BOOL)decelerate {
    if (decelerate == NO) {
        [self autoAdjustScrollToTop];
    }
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    [self autoAdjustScrollToTop];
} 
- (void)autoAdjustScrollToTop {
    // compare the top two visible rows to the current content offset
    // and auto scroll so that the best row is snapped to top
    NSArray *visibleRows = [self.tableView indexPathsForVisibleRows];
    NSIndexPath *firstPath = visibleRows[0];
    NSIndexPath *secondPath = visibleRows[1];
    CGRect firstRowRect = [self.tableView rectForRowAtIndexPath:firstPath];
    [self.tableView scrollToRowAtIndexPath:(firstRowRect.origin.y > self.tableView.contentOffset.y ? firstPath : secondPath) atScrollPosition:UITableViewScrollPositionTop animated:YES];
}