BigDecimal.add() being ignored
<p>I have code like this</p>

<pre><code>BigDecimal withoutTax, tax, withTax, totalPrice;
totalPrice = new BigDecimal(0.0);
BigDecimal amount = new BigDecimal(String.valueOf(table.getValueAt(table.getSelectedRow(), 3)).replace(",", "."));
BigDecimal price = new BigDecimal(String.valueOf(table.getValueAt(table.getSelectedRow(), 4)).replace(",", "."));
withoutTax = amount.multiply(price, new MathContext(5));
table.setValueAt(withoutTax.toPlainString(), table.getSelectedRow(), 5);
tax = withoutTax.multiply(new BigDecimal(0.23), new MathContext(2));
table.setValueAt(tax.toPlainString(), table.getSelectedRow(), 7);
withTax = withoutTax.add(tax, new MathContext(5));
table.setValueAt(withTax.toPlainString(), table.getSelectedRow(), 8);
totalPrice.add(withTax, new MathContext(5));
paymentNum.setText(String.valueOf(totalPrice.toPlainString()));
</code></pre>

<p>why am I receiving that <code>totalPrice.add</code> is ignored while <code>withoutTax.add</code> is working properly?</p>