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	$17.60	6.538%	$18.7507	$18.75	$18.75	$18.80
Purchase #2	$52.86	9.422%	$57.8405	$57.84	$57.85	$57.80
Purchase #3	$160.31	11.178%	$178.2295	$178.23	$178.25	$178.20
Purchase #4	$152.98	6.389%	$162.7539	$162.75	$162.75	$162.80
Purchase #5	$11.95	10.234%	$13.173	$13.17	$13.15	$13.20
Purchase #6	$10.83	8.776%	$11.7804	$11.78	$11.80	$11.80
Purchase #7	$146.69	12.116%	$164.463	$164.46	$164.45	$164.50
7 purchase totals =	$553.22		$606.9910	$606.98	$607.00	$607.10