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	$5.42	9.748%	$5.9483	$5.95	$5.95	$5.90
Purchase #2	$190.72	3.838%	$198.0398	$198.04	$198.05	$198.00
Purchase #3	$38.92	8.272%	$42.1395	$42.14	$42.15	$42.10
Purchase #4	$218.60	4.367%	$228.1463	$228.15	$228.15	$228.10
Purchase #5	$61.47	9.177%	$67.1111	$67.11	$67.10	$67.10
Purchase #6	$120.49	5.286%	$126.8591	$126.86	$126.85	$126.90
Purchase #7	$10.92	8.653%	$11.8649	$11.86	$11.85	$11.90
7 purchase totals =	$646.54		$680.1090	$680.11	$680.10	$680.00