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	$30.49	10.381%	$33.6552	$33.66	$33.65	$33.70
Purchase #2	$159.83	3.470%	$165.3761	$165.38	$165.40	$165.40
Purchase #3	$102.79	8.571%	$111.6001	$111.60	$111.60	$111.60
Purchase #4	$77.38	12.109%	$86.7499	$86.75	$86.75	$86.70
Purchase #5	$166.82	10.551%	$184.4212	$184.42	$184.40	$184.40
Purchase #6	$66.94	9.210%	$73.1052	$73.11	$73.10	$73.10
Purchase #7	$153.33	11.415%	$170.8326	$170.83	$170.85	$170.80
7 purchase totals =	$757.58		$825.7403	$825.75	$825.75	$825.70