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	$114.84	11.536%	$128.0879	$128.09	$128.10	$128.10
Purchase #2	$152.75	4.343%	$159.3839	$159.38	$159.40	$159.40
Purchase #3	$35.36	12.673%	$39.8412	$39.84	$39.85	$39.80
Purchase #4	$100.87	10.121%	$111.0791	$111.08	$111.10	$111.10
Purchase #5	$208.88	6.485%	$222.4259	$222.43	$222.45	$222.40
Purchase #6	$222.99	3.129%	$229.9674	$229.97	$229.95	$230.00
Purchase #7	$55.32	9.219%	$60.42	$60.42	$60.40	$60.40
7 purchase totals =	$891.01		$951.2054	$951.21	$951.25	$951.20