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	$129.43	5.657%	$136.7519	$136.75	$136.75	$136.80
Purchase #2	$132.57	12.162%	$148.6932	$148.69	$148.70	$148.70
Purchase #3	$115.47	10.157%	$127.1983	$127.20	$127.20	$127.20
Purchase #4	$7.91	8.367%	$8.5718	$8.57	$8.55	$8.60
Purchase #5	$80.48	12.584%	$90.6076	$90.61	$90.60	$90.60
Purchase #6	$86.76	4.367%	$90.5488	$90.55	$90.55	$90.50
Purchase #7	$158.99	8.639%	$172.7251	$172.73	$172.75	$172.70
7 purchase totals =	$711.61		$775.0967	$775.10	$775.10	$775.10