You can change the number of decimal places displayed in an individual data cell or for all cells in a row or column. To change the number of decimal places in a data cell, right click on the cell and choose Format (Data Cell). For rows, right click on the Stub and choose Format (Stub). For columns, right click on the column head and choose Format (Column Head).
In all cases, this brings up the Format (table part) dialog. Simply select the number of decimal places for the associated cells, i.e., the row, the column, or the data cell and click OK.

Rows or columns containing percentages are automatically designated as having one decimal place.
If you change the number of decimal places in a data cell to a number other than the default setting (indicated by the word "Default" in the pulldown), then the setting for the data cell will override any settings made for rows or columns containing that data cell. For example, if the data cell is set to one decimal place, and you change the row to have two decimal places, the data cell will still have one decimal place although other cells in the row will change. In order to make the number of decimal places in the data cell follow the number of decimal places set in the row or column, change the setting in the data cell to the default.
You can change the default number of decimal places for data cells in the preferences.