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	$38.43	11.713%	$42.9313	$42.93	$42.95	$42.90
Purchase #2	$65.87	11.509%	$73.451	$73.45	$73.45	$73.50
Purchase #3	$184.86	3.652%	$191.6111	$191.61	$191.60	$191.60
Purchase #4	$159.26	4.525%	$166.4665	$166.47	$166.45	$166.50
Purchase #5	$184.55	8.841%	$200.8661	$200.87	$200.85	$200.90
Purchase #6	$14.26	11.146%	$15.8494	$15.85	$15.85	$15.80
Purchase #7	$190.98	4.537%	$199.6448	$199.64	$199.65	$199.60
7 purchase totals =	$838.21		$890.8202	$890.82	$890.80	$890.80