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	$15.69	11.250%	$17.4551	$17.46	$17.45	$17.50
Purchase #2	$116.72	12.768%	$131.6228	$131.62	$131.60	$131.60
Purchase #3	$153.53	13.429%	$174.1475	$174.15	$174.15	$174.10
Purchase #4	$64.74	13.382%	$73.4035	$73.40	$73.40	$73.40
Purchase #5	$50.52	5.169%	$53.1314	$53.13	$53.15	$53.10
Purchase #6	$239.36	6.713%	$255.4282	$255.43	$255.45	$255.40
Purchase #7	$10.71	3.803%	$11.1173	$11.12	$11.10	$11.10
7 purchase totals =	$651.27		$716.3058	$716.31	$716.30	$716.20