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	$154.25	7.636%	$166.0285	$166.03	$166.05	$166.00
Purchase #2	$103.71	7.420%	$111.4053	$111.41	$111.40	$111.40
Purchase #3	$76.77	4.752%	$80.4181	$80.42	$80.40	$80.40
Purchase #4	$177.44	4.413%	$185.2704	$185.27	$185.25	$185.30
Purchase #5	$161.81	7.313%	$173.6432	$173.64	$173.65	$173.60
Purchase #6	$20.55	3.674%	$21.305	$21.31	$21.30	$21.30
Purchase #7	$57.98	4.265%	$60.4528	$60.45	$60.45	$60.50
7 purchase totals =	$752.51		$798.5233	$798.53	$798.50	$798.50