<ClientSettings>
    <Scrolling ... />
    <ClientEvents OnGridCreated="gridCreated" />
</ClientSettings>

function gridCreated(sender, args) {
    var grid = sender;

//get the header item and set its height
    var HasStaticHeaders = grid.ClientSettings.Scrolling && grid.ClientSettings.Scrolling.UseStaticHeaders;
    var headerRow = HasStaticHeaders ? grid.GridHeaderDiv.querySelector("thead > tr") : grid.get_masterTableView().HeaderRow;

    headerRow.style.height = headerRow.offsetHeight + "px";

//loop through the data items and set height to each of them
    var dataItems = grid.get_masterTableView().get_dataItems();
    var currentItem;

    for (var i = 0; i < dataItems.length; i++) {
        currentItem = dataItems[i].get_element();
        currentItem.style.height = currentItem.offsetHeight + "px";
    }
}