The interval between the gridlines in an Excel chart is typically blank, but you can highlight the intervals using an alternating pattern by changing the formatting for the gridlines themselves.

Here is the data for the ages of customers shopping in the Bitesize CD store. Ages of customers in 1-hour period 25, 29, 45, 19, 36, 17, 60, 51, 39, 24, 15, 13, 31 ...