If the percentage is the same for every row you don't need to include it in the table at all. Example (for row 5 where the %age is 5%):
In A5, the amount.
In B5 =A5*1.05
Then replicate B5 down column B for as many rows as you want.
If you want the ability to vary the percentage, but apply it to every row, simply insert it at the top of the spreadsheet (say in cell A1). Then is (say) row 5:
In A5 the amount
In B5 = A5*$A$1
Then replicate B5 down column B
This will increase all the values you enter in column A by the percentage you enter in cell A1. If you want to change the percentage, simply change it in cell A1.