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	$99.32	12.345%	$111.5811	$111.58	$111.60	$111.60
Purchase #2	$176.67	6.856%	$188.7825	$188.78	$188.80	$188.80
Purchase #3	$10.37	6.648%	$11.0594	$11.06	$11.05	$11.10
Purchase #4	$17.79	12.409%	$19.9976	$20.00	$20.00	$20.00
Purchase #5	$206.36	3.821%	$214.245	$214.25	$214.25	$214.20
Purchase #6	$80.69	13.740%	$91.7768	$91.78	$91.80	$91.80
Purchase #7	$152.32	10.634%	$168.5177	$168.52	$168.50	$168.50
7 purchase totals =	$743.52		$805.9601	$805.97	$806.00	$806.00