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	$202.79	6.245%	$215.4542	$215.45	$215.45	$215.50
Purchase #2	$18.99	12.114%	$21.2904	$21.29	$21.30	$21.30
Purchase #3	$117.62	11.173%	$130.7617	$130.76	$130.75	$130.80
Purchase #4	$54.51	13.240%	$61.7271	$61.73	$61.75	$61.70
Purchase #5	$250.83	11.357%	$279.3168	$279.32	$279.30	$279.30
Purchase #6	$36.75	10.189%	$40.4945	$40.49	$40.50	$40.50
Purchase #7	$235.50	6.732%	$251.3539	$251.35	$251.35	$251.40
7 purchase totals =	$916.99		$1,000.3986	$1,000.39	$1,000.40	$1,000.50