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	$29.66	7.385%	$31.8504	$31.85	$31.85	$31.90
Purchase #2	$122.33	4.719%	$128.1028	$128.10	$128.10	$128.10
Purchase #3	$127.32	3.433%	$131.6909	$131.69	$131.70	$131.70
Purchase #4	$95.81	8.284%	$103.7469	$103.75	$103.75	$103.70
Purchase #5	$102.70	8.378%	$111.3042	$111.30	$111.30	$111.30
Purchase #6	$47.60	4.143%	$49.5721	$49.57	$49.55	$49.60
Purchase #7	$118.47	13.848%	$134.8757	$134.88	$134.90	$134.90
7 purchase totals =	$643.89		$691.1430	$691.14	$691.15	$691.20