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	$37.98	6.152%	$40.3165	$40.32	$40.30	$40.30
Purchase #2	$76.83	4.286%	$80.1229	$80.12	$80.10	$80.10
Purchase #3	$205.86	8.468%	$223.2922	$223.29	$223.30	$223.30
Purchase #4	$241.93	11.843%	$270.5818	$270.58	$270.60	$270.60
Purchase #5	$48.66	13.629%	$55.2919	$55.29	$55.30	$55.30
Purchase #6	$247.71	7.170%	$265.4708	$265.47	$265.45	$265.50
Purchase #7	$26.87	5.439%	$28.3315	$28.33	$28.35	$28.30
7 purchase totals =	$885.84		$963.4076	$963.40	$963.40	$963.40