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	$30.83	10.661%	$34.1168	$34.12	$34.10	$34.10
Purchase #2	$48.79	12.856%	$55.0624	$55.06	$55.05	$55.10
Purchase #3	$93.55	12.183%	$104.9472	$104.95	$104.95	$104.90
Purchase #4	$54.32	4.160%	$56.5797	$56.58	$56.60	$56.60
Purchase #5	$11.35	3.711%	$11.7712	$11.77	$11.75	$11.80
Purchase #6	$67.79	6.413%	$72.1374	$72.14	$72.15	$72.10
Purchase #7	$113.67	7.196%	$121.8497	$121.85	$121.85	$121.80
7 purchase totals =	$420.30		$456.4644	$456.47	$456.45	$456.40