private void Calculate()
{
dataGridViewStocks_CellValueChanged(null, null);
textBoxAmount.Text = summaryAmount.ToString(Program.NUMBER_FORMAT);
textBoxVat.Text = summaryVat.ToString(Program.NUMBER_FORMAT);
textBoxCityTax.Text = summaryCityTax.ToString(Program.NUMBER_FORMAT);
textBoxNonCash.Text = summaryNonCash.ToString(Program.NUMBER_FORMAT);
textBoxCash.Text = (summaryAmount - summaryNonCash < 0 ? 0 : summaryAmount - summaryNonCash).ToString(Program.NUMBER_FORMAT);
textBoxPaidAmount.Text = textBoxCash.Text;
}