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	$139.73	8.478%	$151.5763	$151.58	$151.60	$151.60
Purchase #2	$72.40	13.595%	$82.2428	$82.24	$82.25	$82.20
Purchase #3	$239.67	11.446%	$267.1026	$267.10	$267.10	$267.10
Purchase #4	$131.99	6.856%	$141.0392	$141.04	$141.05	$141.00
Purchase #5	$137.72	6.606%	$146.8178	$146.82	$146.80	$146.80
Purchase #6	$108.31	11.766%	$121.0538	$121.05	$121.05	$121.10
Purchase #7	$183.61	3.536%	$190.1024	$190.10	$190.10	$190.10
7 purchase totals =	$1,013.43		$1,099.9349	$1,099.93	$1,099.95	$1,099.90