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	$94.83	9.434%	$103.7763	$103.78	$103.80	$103.80
Purchase #2	$105.56	10.764%	$116.9225	$116.92	$116.90	$116.90
Purchase #3	$200.70	11.258%	$223.2948	$223.29	$223.30	$223.30
Purchase #4	$40.79	10.189%	$44.9461	$44.95	$44.95	$44.90
Purchase #5	$93.49	7.520%	$100.5204	$100.52	$100.50	$100.50
Purchase #6	$219.43	3.235%	$226.5286	$226.53	$226.55	$226.50
Purchase #7	$50.87	6.251%	$54.0499	$54.05	$54.05	$54.00
7 purchase totals =	$805.67		$870.0386	$870.04	$870.05	$869.90