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	$36.44	9.867%	$40.0355	$40.04	$40.05	$40.00
Purchase #2	$85.41	4.612%	$89.3491	$89.35	$89.35	$89.30
Purchase #3	$9.77	9.353%	$10.6838	$10.68	$10.70	$10.70
Purchase #4	$188.52	5.160%	$198.2476	$198.25	$198.25	$198.20
Purchase #5	$56.57	10.841%	$62.7028	$62.70	$62.70	$62.70
Purchase #6	$85.65	3.675%	$88.7976	$88.80	$88.80	$88.80
Purchase #7	$67.83	4.322%	$70.7616	$70.76	$70.75	$70.80
7 purchase totals =	$530.19		$560.5780	$560.58	$560.60	$560.50