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	$242.78	3.313%	$250.8233	$250.82	$250.80	$250.80
Purchase #2	$248.66	11.778%	$277.9472	$277.95	$277.95	$277.90
Purchase #3	$105.66	5.509%	$111.4808	$111.48	$111.50	$111.50
Purchase #4	$188.87	5.501%	$199.2597	$199.26	$199.25	$199.30
Purchase #5	$29.33	5.381%	$30.9082	$30.91	$30.90	$30.90
Purchase #6	$26.47	4.777%	$27.7345	$27.73	$27.75	$27.70
Purchase #7	$159.80	7.793%	$172.2532	$172.25	$172.25	$172.30
7 purchase totals =	$1,001.57		$1,070.4069	$1,070.40	$1,070.40	$1,070.40