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	$63.64	12.617%	$71.6695	$71.67	$71.65	$71.70
Purchase #2	$122.45	3.844%	$127.157	$127.16	$127.15	$127.20
Purchase #3	$72.57	10.287%	$80.0353	$80.04	$80.05	$80.00
Purchase #4	$116.40	12.332%	$130.7544	$130.75	$130.75	$130.80
Purchase #5	$165.69	11.420%	$184.6118	$184.61	$184.60	$184.60
Purchase #6	$184.57	11.648%	$206.0687	$206.07	$206.05	$206.10
Purchase #7	$31.62	9.158%	$34.5158	$34.52	$34.50	$34.50
7 purchase totals =	$756.94		$834.8125	$834.82	$834.75	$834.90