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	$203.76	7.177%	$218.3839	$218.38	$218.40	$218.40
Purchase #2	$131.75	11.255%	$146.5785	$146.58	$146.60	$146.60
Purchase #3	$5.94	11.261%	$6.6089	$6.61	$6.60	$6.60
Purchase #4	$12.98	10.669%	$14.3648	$14.36	$14.35	$14.40
Purchase #5	$18.38	3.400%	$19.0049	$19.00	$19.00	$19.00
Purchase #6	$103.81	7.346%	$111.4359	$111.44	$111.45	$111.40
Purchase #7	$75.25	9.620%	$82.4891	$82.49	$82.50	$82.50
7 purchase totals =	$551.87		$598.8660	$598.86	$598.90	$598.90