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	$105.50	12.406%	$118.5883	$118.59	$118.60	$118.60
Purchase #2	$20.54	10.576%	$22.7123	$22.71	$22.70	$22.70
Purchase #3	$114.98	10.560%	$127.1219	$127.12	$127.10	$127.10
Purchase #4	$139.95	12.836%	$157.914	$157.91	$157.90	$157.90
Purchase #5	$14.71	11.639%	$16.4221	$16.42	$16.40	$16.40
Purchase #6	$33.75	10.429%	$37.2698	$37.27	$37.25	$37.30
Purchase #7	$144.93	10.321%	$159.8882	$159.89	$159.90	$159.90
7 purchase totals =	$574.36		$639.9166	$639.91	$639.85	$639.90