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	$234.29	10.304%	$258.4312	$258.43	$258.45	$258.40
Purchase #2	$240.91	4.808%	$252.493	$252.49	$252.50	$252.50
Purchase #3	$109.31	12.618%	$123.1027	$123.10	$123.10	$123.10
Purchase #4	$82.74	4.574%	$86.5245	$86.52	$86.50	$86.50
Purchase #5	$29.34	10.285%	$32.3576	$32.36	$32.35	$32.40
Purchase #6	$163.56	5.274%	$172.1862	$172.19	$172.20	$172.20
Purchase #7	$60.56	9.833%	$66.5149	$66.51	$66.50	$66.50
7 purchase totals =	$920.71		$991.6101	$991.60	$991.60	$991.60