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	$18.96	11.634%	$21.1658	$21.17	$21.15	$21.20
Purchase #2	$169.81	11.838%	$189.9121	$189.91	$189.90	$189.90
Purchase #3	$7.50	6.184%	$7.9638	$7.96	$7.95	$8.00
Purchase #4	$153.86	11.851%	$172.0939	$172.09	$172.10	$172.10
Purchase #5	$38.34	12.847%	$43.2655	$43.27	$43.25	$43.30
Purchase #6	$21.70	13.358%	$24.5987	$24.60	$24.60	$24.60
Purchase #7	$146.84	12.688%	$165.4711	$165.47	$165.45	$165.50
7 purchase totals =	$557.01		$624.4709	$624.47	$624.40	$624.60