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	$56.40	9.297%	$61.6435	$61.64	$61.65	$61.60
Purchase #2	$183.45	9.270%	$200.4558	$200.46	$200.45	$200.50
Purchase #3	$115.72	6.601%	$123.3587	$123.36	$123.35	$123.40
Purchase #4	$77.81	13.806%	$88.5524	$88.55	$88.55	$88.60
Purchase #5	$34.62	8.661%	$37.6184	$37.62	$37.60	$37.60
Purchase #6	$48.40	9.216%	$52.8605	$52.86	$52.85	$52.90
Purchase #7	$72.79	4.313%	$75.9294	$75.93	$75.95	$75.90
7 purchase totals =	$589.19		$640.4187	$640.42	$640.40	$640.50