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	$111.84	10.323%	$123.3852	$123.39	$123.40	$123.40
Purchase #2	$53.75	10.305%	$59.2889	$59.29	$59.30	$59.30
Purchase #3	$159.86	7.862%	$172.4282	$172.43	$172.45	$172.40
Purchase #4	$237.59	6.292%	$252.5392	$252.54	$252.55	$252.50
Purchase #5	$225.71	5.810%	$238.8238	$238.82	$238.80	$238.80
Purchase #6	$44.92	8.137%	$48.5751	$48.58	$48.60	$48.60
Purchase #7	$60.50	7.159%	$64.8312	$64.83	$64.85	$64.80
7 purchase totals =	$894.17		$959.8716	$959.88	$959.95	$959.80