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	$37.48	10.221%	$41.3108	$41.31	$41.30	$41.30
Purchase #2	$48.52	4.237%	$50.5758	$50.58	$50.60	$50.60
Purchase #3	$222.65	3.563%	$230.583	$230.58	$230.60	$230.60
Purchase #4	$17.94	10.235%	$19.7762	$19.78	$19.80	$19.80
Purchase #5	$37.86	6.718%	$40.4034	$40.40	$40.40	$40.40
Purchase #6	$131.51	4.835%	$137.8685	$137.87	$137.85	$137.90
Purchase #7	$48.87	7.580%	$52.5743	$52.57	$52.55	$52.60
7 purchase totals =	$544.83		$573.0920	$573.09	$573.10	$573.20