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	$85.88	6.546%	$91.5017	$91.50	$91.50	$91.50
Purchase #2	$48.50	13.854%	$55.2192	$55.22	$55.20	$55.20
Purchase #3	$69.71	3.519%	$72.1631	$72.16	$72.15	$72.20
Purchase #4	$70.57	5.466%	$74.4274	$74.43	$74.45	$74.40
Purchase #5	$228.73	8.186%	$247.4538	$247.45	$247.45	$247.50
Purchase #6	$29.73	9.724%	$32.6209	$32.62	$32.60	$32.60
Purchase #7	$56.81	9.615%	$62.2723	$62.27	$62.25	$62.30
7 purchase totals =	$589.93		$635.6584	$635.65	$635.60	$635.70