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	$94.86	8.111%	$102.5541	$102.55	$102.55	$102.60
Purchase #2	$211.35	13.237%	$239.3264	$239.33	$239.35	$239.30
Purchase #3	$97.72	7.308%	$104.8614	$104.86	$104.85	$104.90
Purchase #4	$11.32	11.333%	$12.6029	$12.60	$12.60	$12.60
Purchase #5	$77.69	7.468%	$83.4919	$83.49	$83.50	$83.50
Purchase #6	$145.62	10.300%	$160.6189	$160.62	$160.60	$160.60
Purchase #7	$176.51	3.377%	$182.4707	$182.47	$182.45	$182.50
7 purchase totals =	$815.07		$885.9263	$885.92	$885.90	$886.00