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	$35.84	8.697%	$38.957	$38.96	$38.95	$39.00
Purchase #2	$130.60	9.117%	$142.5068	$142.51	$142.50	$142.50
Purchase #3	$54.59	5.431%	$57.5548	$57.55	$57.55	$57.60
Purchase #4	$63.60	3.498%	$65.8247	$65.82	$65.80	$65.80
Purchase #5	$125.50	13.553%	$142.509	$142.51	$142.50	$142.50
Purchase #6	$76.59	9.289%	$83.7044	$83.70	$83.70	$83.70
Purchase #7	$44.34	9.325%	$48.4747	$48.47	$48.45	$48.50
7 purchase totals =	$531.06		$579.5314	$579.52	$579.45	$579.60