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	$52.63	3.507%	$54.4757	$54.48	$54.50	$54.50
Purchase #2	$40.80	8.795%	$44.3884	$44.39	$44.40	$44.40
Purchase #3	$161.45	13.561%	$183.3442	$183.34	$183.35	$183.30
Purchase #4	$30.52	8.174%	$33.0147	$33.01	$33.00	$33.00
Purchase #5	$44.53	7.308%	$47.7843	$47.78	$47.80	$47.80
Purchase #6	$37.72	7.286%	$40.4683	$40.47	$40.45	$40.50
Purchase #7	$90.83	11.287%	$101.082	$101.08	$101.10	$101.10
7 purchase totals =	$458.48		$504.5576	$504.55	$504.60	$504.60