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	$247.51	3.278%	$255.6234	$255.62	$255.60	$255.60
Purchase #2	$103.81	13.700%	$118.032	$118.03	$118.05	$118.00
Purchase #3	$229.33	10.209%	$252.7423	$252.74	$252.75	$252.70
Purchase #4	$245.29	4.466%	$256.2447	$256.24	$256.25	$256.20
Purchase #5	$77.40	10.305%	$85.3761	$85.38	$85.40	$85.40
Purchase #6	$208.75	7.495%	$224.3958	$224.40	$224.40	$224.40
Purchase #7	$120.62	5.785%	$127.5979	$127.60	$127.60	$127.60
7 purchase totals =	$1,232.71		$1,320.0122	$1,320.01	$1,320.05	$1,319.90