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	$198.83	11.403%	$221.5026	$221.50	$221.50	$221.50
Purchase #2	$154.82	13.370%	$175.5194	$175.52	$175.50	$175.50
Purchase #3	$66.95	10.319%	$73.8586	$73.86	$73.85	$73.90
Purchase #4	$101.81	6.539%	$108.4674	$108.47	$108.45	$108.50
Purchase #5	$60.32	12.388%	$67.7924	$67.79	$67.80	$67.80
Purchase #6	$185.59	13.178%	$210.0471	$210.05	$210.05	$210.00
Purchase #7	$53.58	10.518%	$59.2155	$59.22	$59.20	$59.20
7 purchase totals =	$821.90		$916.4030	$916.41	$916.35	$916.40