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	$223.72	6.594%	$238.4721	$238.47	$238.45	$238.50
Purchase #2	$150.95	9.562%	$165.3838	$165.38	$165.40	$165.40
Purchase #3	$192.85	6.397%	$205.1866	$205.19	$205.20	$205.20
Purchase #4	$158.54	5.132%	$166.6763	$166.68	$166.70	$166.70
Purchase #5	$122.86	4.235%	$128.0631	$128.06	$128.05	$128.10
Purchase #6	$196.94	13.655%	$223.8322	$223.83	$223.85	$223.80
Purchase #7	$157.72	11.243%	$175.4525	$175.45	$175.45	$175.50
7 purchase totals =	$1,203.58		$1,303.0666	$1,303.06	$1,303.10	$1,303.20