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	$200.78	10.286%	$221.4322	$221.43	$221.45	$221.40
Purchase #2	$130.69	11.319%	$145.4828	$145.48	$145.50	$145.50
Purchase #3	$217.60	3.518%	$225.2552	$225.26	$225.25	$225.30
Purchase #4	$79.63	13.528%	$90.4023	$90.40	$90.40	$90.40
Purchase #5	$149.76	10.222%	$165.0685	$165.07	$165.05	$165.10
Purchase #6	$84.65	12.706%	$95.4056	$95.41	$95.40	$95.40
Purchase #7	$40.92	3.554%	$42.3743	$42.37	$42.35	$42.40
7 purchase totals =	$904.03		$985.4209	$985.42	$985.40	$985.50