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	$87.52	12.155%	$98.1581	$98.16	$98.15	$98.20
Purchase #2	$122.95	9.660%	$134.827	$134.83	$134.85	$134.80
Purchase #3	$86.70	5.523%	$91.4884	$91.49	$91.50	$91.50
Purchase #4	$37.72	13.708%	$42.8907	$42.89	$42.90	$42.90
Purchase #5	$172.44	10.467%	$190.4893	$190.49	$190.50	$190.50
Purchase #6	$97.26	8.478%	$105.5057	$105.51	$105.50	$105.50
Purchase #7	$75.42	10.872%	$83.6197	$83.62	$83.60	$83.60
7 purchase totals =	$680.01		$746.9789	$746.99	$747.00	$747.00