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	$58.78	9.132%	$64.1478	$64.15	$64.15	$64.10
Purchase #2	$52.62	5.485%	$55.5062	$55.51	$55.50	$55.50
Purchase #3	$173.52	5.345%	$182.7946	$182.79	$182.80	$182.80
Purchase #4	$37.80	11.353%	$42.0914	$42.09	$42.10	$42.10
Purchase #5	$242.33	13.818%	$275.8152	$275.82	$275.80	$275.80
Purchase #6	$18.50	7.177%	$19.8277	$19.83	$19.85	$19.80
Purchase #7	$70.48	10.490%	$77.8734	$77.87	$77.85	$77.90
7 purchase totals =	$654.03		$718.0563	$718.06	$718.05	$718.00