Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$19.48	8.724%	$21.1794	$21.18	$21.20	$21.20
Purchase #2	$95.86	12.730%	$108.063	$108.06	$108.05	$108.10
Purchase #3	$115.89	6.407%	$123.3151	$123.32	$123.30	$123.30
Purchase #4	$45.32	6.836%	$48.4181	$48.42	$48.40	$48.40
Purchase #5	$245.96	4.237%	$256.3813	$256.38	$256.40	$256.40
Purchase #6	$103.88	6.618%	$110.7548	$110.75	$110.75	$110.80
Purchase #7	$246.42	3.582%	$255.2468	$255.25	$255.25	$255.20
7 purchase totals =	$872.81		$923.3585	$923.36	$923.35	$923.40