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	$76.77	9.378%	$83.9695	$83.97	$83.95	$84.00
Purchase #2	$69.83	12.255%	$78.3877	$78.39	$78.40	$78.40
Purchase #3	$116.90	7.849%	$126.0755	$126.08	$126.10	$126.10
Purchase #4	$37.98	9.564%	$41.6124	$41.61	$41.60	$41.60
Purchase #5	$100.75	8.869%	$109.6855	$109.69	$109.70	$109.70
Purchase #6	$74.97	3.864%	$77.8668	$77.87	$77.85	$77.90
Purchase #7	$150.46	10.440%	$166.168	$166.17	$166.15	$166.20
7 purchase totals =	$627.66		$683.7654	$683.78	$683.75	$683.90