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	$204.58	7.744%	$220.4227	$220.42	$220.40	$220.40
Purchase #2	$119.61	8.285%	$129.5197	$129.52	$129.50	$129.50
Purchase #3	$171.93	10.287%	$189.6164	$189.62	$189.60	$189.60
Purchase #4	$137.80	5.555%	$145.4548	$145.45	$145.45	$145.50
Purchase #5	$75.83	13.188%	$85.8305	$85.83	$85.85	$85.80
Purchase #6	$49.55	11.182%	$55.0907	$55.09	$55.10	$55.10
Purchase #7	$35.72	4.390%	$37.2881	$37.29	$37.30	$37.30
7 purchase totals =	$795.02		$863.2229	$863.22	$863.20	$863.20