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	$49.88	13.379%	$56.5534	$56.55	$56.55	$56.60
Purchase #2	$154.62	7.701%	$166.5273	$166.53	$166.55	$166.50
Purchase #3	$205.30	10.302%	$226.45	$226.45	$226.45	$226.50
Purchase #4	$205.73	4.245%	$214.4632	$214.46	$214.45	$214.50
Purchase #5	$173.77	5.678%	$183.6367	$183.64	$183.65	$183.60
Purchase #6	$28.47	12.156%	$31.9308	$31.93	$31.95	$31.90
Purchase #7	$243.91	11.471%	$271.8889	$271.89	$271.90	$271.90
7 purchase totals =	$1,061.68		$1,151.4503	$1,151.45	$1,151.50	$1,151.50