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	$7.75	4.648%	$8.1102	$8.11	$8.10	$8.10
Purchase #2	$60.63	5.385%	$63.8949	$63.89	$63.90	$63.90
Purchase #3	$85.69	6.377%	$91.1545	$91.15	$91.15	$91.20
Purchase #4	$108.92	10.398%	$120.2455	$120.25	$120.25	$120.20
Purchase #5	$180.59	5.390%	$190.3238	$190.32	$190.30	$190.30
Purchase #6	$16.61	11.748%	$18.5613	$18.56	$18.55	$18.60
Purchase #7	$122.94	13.485%	$139.5185	$139.52	$139.50	$139.50
7 purchase totals =	$583.13		$631.8087	$631.80	$631.75	$631.80