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	$51.65	11.639%	$57.6615	$57.66	$57.65	$57.70
Purchase #2	$151.66	13.832%	$172.6376	$172.64	$172.65	$172.60
Purchase #3	$166.36	4.123%	$173.219	$173.22	$173.20	$173.20
Purchase #4	$163.64	5.366%	$172.4209	$172.42	$172.40	$172.40
Purchase #5	$190.40	10.357%	$210.1197	$210.12	$210.10	$210.10
Purchase #6	$98.43	13.147%	$111.3706	$111.37	$111.35	$111.40
Purchase #7	$49.76	12.828%	$56.1432	$56.14	$56.15	$56.10
7 purchase totals =	$871.90		$953.5725	$953.57	$953.50	$953.50