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	$53.26	6.196%	$56.56	$56.56	$56.55	$56.60
Purchase #2	$154.60	11.314%	$172.0914	$172.09	$172.10	$172.10
Purchase #3	$238.61	7.600%	$256.7444	$256.74	$256.75	$256.70
Purchase #4	$116.42	9.140%	$127.0608	$127.06	$127.05	$127.10
Purchase #5	$21.52	4.601%	$22.5101	$22.51	$22.50	$22.50
Purchase #6	$63.31	6.572%	$67.4707	$67.47	$67.45	$67.50
Purchase #7	$129.67	7.737%	$139.7026	$139.70	$139.70	$139.70
7 purchase totals =	$777.39		$842.1400	$842.13	$842.10	$842.20