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	$41.27	3.772%	$42.8267	$42.83	$42.85	$42.80
Purchase #2	$77.82	7.176%	$83.4044	$83.40	$83.40	$83.40
Purchase #3	$237.51	10.286%	$261.9403	$261.94	$261.95	$261.90
Purchase #4	$9.38	11.354%	$10.445	$10.45	$10.45	$10.40
Purchase #5	$21.75	13.209%	$24.623	$24.62	$24.60	$24.60
Purchase #6	$118.27	4.640%	$123.7577	$123.76	$123.75	$123.80
Purchase #7	$66.97	10.653%	$74.1043	$74.10	$74.10	$74.10
7 purchase totals =	$572.97		$621.1014	$621.10	$621.10	$621.00