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	$12.39	10.350%	$13.6724	$13.67	$13.65	$13.70
Purchase #2	$229.77	11.187%	$255.4744	$255.47	$255.45	$255.50
Purchase #3	$33.42	7.387%	$35.8887	$35.89	$35.90	$35.90
Purchase #4	$169.83	11.741%	$189.7697	$189.77	$189.75	$189.80
Purchase #5	$24.56	5.237%	$25.8462	$25.85	$25.85	$25.80
Purchase #6	$159.72	4.643%	$167.1358	$167.14	$167.15	$167.10
Purchase #7	$120.78	11.233%	$134.3472	$134.35	$134.35	$134.30
7 purchase totals =	$750.47		$822.1344	$822.14	$822.10	$822.10