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	$19.49	6.277%	$20.7134	$20.71	$20.70	$20.70
Purchase #2	$118.63	13.126%	$134.2014	$134.20	$134.20	$134.20
Purchase #3	$142.30	6.325%	$151.3005	$151.30	$151.30	$151.30
Purchase #4	$75.43	8.784%	$82.0558	$82.06	$82.05	$82.10
Purchase #5	$111.91	4.396%	$116.8296	$116.83	$116.85	$116.80
Purchase #6	$128.27	10.665%	$141.95	$141.95	$141.95	$142.00
Purchase #7	$173.25	5.365%	$182.5449	$182.54	$182.55	$182.50
7 purchase totals =	$769.28		$829.5956	$829.59	$829.60	$829.60