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	$128.38	6.837%	$137.1573	$137.16	$137.15	$137.20
Purchase #2	$166.39	10.277%	$183.4899	$183.49	$183.50	$183.50
Purchase #3	$243.99	10.632%	$269.931	$269.93	$269.95	$269.90
Purchase #4	$138.41	11.528%	$154.3659	$154.37	$154.35	$154.40
Purchase #5	$155.35	4.747%	$162.7245	$162.72	$162.70	$162.70
Purchase #6	$105.31	12.638%	$118.6191	$118.62	$118.60	$118.60
Purchase #7	$111.90	13.855%	$127.4037	$127.40	$127.40	$127.40
7 purchase totals =	$1,049.73		$1,153.6914	$1,153.69	$1,153.65	$1,153.70