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	$41.42	3.385%	$42.8221	$42.82	$42.80	$42.80
Purchase #2	$102.55	13.305%	$116.1943	$116.19	$116.20	$116.20
Purchase #3	$147.84	7.792%	$159.3597	$159.36	$159.35	$159.40
Purchase #4	$100.74	10.280%	$111.0961	$111.10	$111.10	$111.10
Purchase #5	$151.82	13.363%	$172.1077	$172.11	$172.10	$172.10
Purchase #6	$8.53	10.193%	$9.3995	$9.40	$9.40	$9.40
Purchase #7	$34.62	12.743%	$39.0316	$39.03	$39.05	$39.00
7 purchase totals =	$587.52		$650.0110	$650.01	$650.00	$650.00