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	$141.68	11.850%	$158.4691	$158.47	$158.45	$158.50
Purchase #2	$95.73	5.112%	$100.6237	$100.62	$100.60	$100.60
Purchase #3	$78.76	6.661%	$84.0062	$84.01	$84.00	$84.00
Purchase #4	$191.58	4.484%	$200.1704	$200.17	$200.15	$200.20
Purchase #5	$221.66	11.798%	$247.8114	$247.81	$247.80	$247.80
Purchase #6	$11.46	9.245%	$12.5195	$12.52	$12.50	$12.50
Purchase #7	$170.38	8.784%	$185.3462	$185.35	$185.35	$185.30
7 purchase totals =	$911.25		$988.9465	$988.95	$988.85	$988.90