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	$155.33	7.258%	$166.6039	$166.60	$166.60	$166.60
Purchase #2	$114.67	3.680%	$118.8899	$118.89	$118.90	$118.90
Purchase #3	$104.70	5.826%	$110.7998	$110.80	$110.80	$110.80
Purchase #4	$230.49	10.687%	$255.1225	$255.12	$255.10	$255.10
Purchase #5	$194.40	10.277%	$214.3785	$214.38	$214.40	$214.40
Purchase #6	$59.25	12.213%	$66.4862	$66.49	$66.50	$66.50
Purchase #7	$139.75	8.592%	$151.7573	$151.76	$151.75	$151.80
7 purchase totals =	$998.59		$1,084.0381	$1,084.04	$1,084.05	$1,084.10