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	$167.84	6.446%	$178.659	$178.66	$178.65	$178.70
Purchase #2	$38.76	8.772%	$42.16	$42.16	$42.15	$42.20
Purchase #3	$83.35	6.341%	$88.6352	$88.64	$88.65	$88.60
Purchase #4	$117.93	10.464%	$130.2702	$130.27	$130.25	$130.30
Purchase #5	$142.74	6.430%	$151.9182	$151.92	$151.90	$151.90
Purchase #6	$12.53	4.668%	$13.1149	$13.11	$13.10	$13.10
Purchase #7	$38.89	7.356%	$41.7507	$41.75	$41.75	$41.80
7 purchase totals =	$602.04		$646.5082	$646.51	$646.45	$646.60