GridViewDecimalColumn offers the DecimalPlaces property which specifies how many decimal places to be shown in the numeric values. However, this doesn't seem to be suitable for your scenario.
The appropriate way to achieve different format of the cells belonging to the same column is to use the CellFormatting event and specify the CellElement.Text considering cell's Value, RowInfo and ColumnInfo. Setting the CellElement.Text actually indicates what text to be shown in the cells.
I hope this information helps. If you need any further assistance please don't hesitate to contact me.
Dess | Tech Support Engineer, Sr.