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	$46.46	12.258%	$52.1551	$52.16	$52.15	$52.20
Purchase #2	$19.46	8.519%	$21.1178	$21.12	$21.10	$21.10
Purchase #3	$78.26	12.777%	$88.2593	$88.26	$88.25	$88.30
Purchase #4	$100.43	11.480%	$111.9594	$111.96	$111.95	$112.00
Purchase #5	$198.83	5.380%	$209.5271	$209.53	$209.55	$209.50
Purchase #6	$63.60	4.149%	$66.2388	$66.24	$66.25	$66.20
Purchase #7	$57.27	11.712%	$63.9775	$63.98	$64.00	$64.00
7 purchase totals =	$564.31		$613.2350	$613.25	$613.25	$613.30