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	$204.65	9.189%	$223.4553	$223.46	$223.45	$223.50
Purchase #2	$175.49	4.352%	$183.1273	$183.13	$183.15	$183.10
Purchase #3	$232.53	13.583%	$264.1145	$264.11	$264.10	$264.10
Purchase #4	$244.35	9.553%	$267.6928	$267.69	$267.70	$267.70
Purchase #5	$177.49	10.545%	$196.2063	$196.21	$196.20	$196.20
Purchase #6	$52.54	8.169%	$56.832	$56.83	$56.85	$56.80
Purchase #7	$248.47	7.414%	$266.8916	$266.89	$266.90	$266.90
7 purchase totals =	$1,335.52		$1,458.3198	$1,458.32	$1,458.35	$1,458.30