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	$38.56	6.551%	$41.0861	$41.09	$41.10	$41.10
Purchase #2	$48.95	7.828%	$52.7818	$52.78	$52.80	$52.80
Purchase #3	$10.35	4.109%	$10.7753	$10.78	$10.80	$10.80
Purchase #4	$82.34	8.160%	$89.0589	$89.06	$89.05	$89.10
Purchase #5	$38.72	10.530%	$42.7972	$42.80	$42.80	$42.80
Purchase #6	$217.48	6.296%	$231.1725	$231.17	$231.15	$231.20
Purchase #7	$54.63	11.413%	$60.8649	$60.86	$60.85	$60.90
7 purchase totals =	$491.03		$528.5367	$528.54	$528.55	$528.70