Custom Tax Calculation Error

I just set a custom tax rate 2.5% when I create the invoice inclusive the tax rate, the system calculation is not 2.5% but 2.4390244% could you have a look in this problem.

5,000,000 --> 2.5% = 125,000, however what appeared is 121,951.22

There is nothing wrong with the calculation:
Tax inclusive 4.878,048.78 @ 2.5 = 121,951.22 or 5,000,000
Tax exclusive 5,000,000 @ 2.5 = 125.000 or 5,125,000

To be clear, tax-inclusive transactions back the tax out of the amount entered, automatically figuring what the taxed amount would have been to produce the amount entered at the tax rate listed.

Tax-exclusive transactions add the specified tax to the amount entered.