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	$46.66	9.554%	$51.1179	$51.12	$51.10	$51.10
Purchase #2	$11.28	7.143%	$12.0857	$12.09	$12.10	$12.10
Purchase #3	$126.34	6.446%	$134.4839	$134.48	$134.50	$134.50
Purchase #4	$19.39	10.862%	$21.4961	$21.50	$21.50	$21.50
Purchase #5	$149.42	3.203%	$154.2059	$154.21	$154.20	$154.20
Purchase #6	$102.32	9.256%	$111.7907	$111.79	$111.80	$111.80
Purchase #7	$57.32	12.663%	$64.5784	$64.58	$64.60	$64.60
7 purchase totals =	$512.73		$549.7586	$549.77	$549.80	$549.80