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	$38.56	6.679%	$41.1354	$41.14	$41.15	$41.10
Purchase #2	$105.94	10.167%	$116.7109	$116.71	$116.70	$116.70
Purchase #3	$71.66	11.578%	$79.9568	$79.96	$79.95	$80.00
Purchase #4	$42.59	13.709%	$48.4287	$48.43	$48.45	$48.40
Purchase #5	$64.95	11.564%	$72.4608	$72.46	$72.45	$72.50
Purchase #6	$19.93	4.481%	$20.8231	$20.82	$20.80	$20.80
Purchase #7	$88.66	11.750%	$99.0776	$99.08	$99.10	$99.10
7 purchase totals =	$432.29		$478.5933	$478.60	$478.60	$478.60