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	$116.82	10.426%	$128.9997	$129.00	$129.00	$129.00
Purchase #2	$165.32	4.331%	$172.48	$172.48	$172.50	$172.50
Purchase #3	$138.32	13.299%	$156.7152	$156.72	$156.70	$156.70
Purchase #4	$158.83	7.195%	$170.2578	$170.26	$170.25	$170.30
Purchase #5	$48.77	12.666%	$54.9472	$54.95	$54.95	$54.90
Purchase #6	$10.74	3.708%	$11.1382	$11.14	$11.15	$11.10
Purchase #7	$105.89	4.229%	$110.3681	$110.37	$110.35	$110.40
7 purchase totals =	$744.69		$804.9062	$804.92	$804.90	$804.90