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	$90.84	10.487%	$100.3664	$100.37	$100.35	$100.40
Purchase #2	$65.40	13.686%	$74.3506	$74.35	$74.35	$74.40
Purchase #3	$56.86	4.848%	$59.6166	$59.62	$59.60	$59.60
Purchase #4	$47.43	10.676%	$52.4936	$52.49	$52.50	$52.50
Purchase #5	$63.71	3.179%	$65.7353	$65.74	$65.75	$65.70
Purchase #6	$80.67	8.800%	$87.769	$87.77	$87.75	$87.80
Purchase #7	$218.60	4.429%	$228.2818	$228.28	$228.30	$228.30
7 purchase totals =	$623.51		$668.6133	$668.62	$668.60	$668.70