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	$73.79	9.763%	$80.9941	$80.99	$81.00	$81.00
Purchase #2	$138.26	12.555%	$155.6185	$155.62	$155.60	$155.60
Purchase #3	$151.81	11.230%	$168.8583	$168.86	$168.85	$168.90
Purchase #4	$160.45	3.135%	$165.4801	$165.48	$165.50	$165.50
Purchase #5	$221.48	13.174%	$250.6578	$250.66	$250.65	$250.70
Purchase #6	$159.60	8.338%	$172.9074	$172.91	$172.90	$172.90
Purchase #7	$6.83	10.831%	$7.5698	$7.57	$7.55	$7.60
7 purchase totals =	$912.22		$1,002.0860	$1,002.09	$1,002.05	$1,002.20