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	$205.43	6.413%	$218.6042	$218.60	$218.60	$218.60
Purchase #2	$40.69	13.482%	$46.1758	$46.18	$46.20	$46.20
Purchase #3	$52.41	8.433%	$56.8297	$56.83	$56.85	$56.80
Purchase #4	$170.90	11.369%	$190.3296	$190.33	$190.35	$190.30
Purchase #5	$14.87	11.213%	$16.5374	$16.54	$16.55	$16.50
Purchase #6	$33.85	10.773%	$37.4967	$37.50	$37.50	$37.50
Purchase #7	$94.86	10.176%	$104.513	$104.51	$104.50	$104.50
7 purchase totals =	$613.01		$670.4864	$670.49	$670.55	$670.40