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	$25.94	13.307%	$29.3918	$29.39	$29.40	$29.40
Purchase #2	$86.72	9.358%	$94.8353	$94.84	$94.85	$94.80
Purchase #3	$22.81	13.201%	$25.8211	$25.82	$25.80	$25.80
Purchase #4	$153.36	3.152%	$158.1939	$158.19	$158.20	$158.20
Purchase #5	$60.79	8.210%	$65.7809	$65.78	$65.80	$65.80
Purchase #6	$115.71	6.574%	$123.3168	$123.32	$123.30	$123.30
Purchase #7	$12.92	5.322%	$13.6076	$13.61	$13.60	$13.60
7 purchase totals =	$478.25		$510.9474	$510.95	$510.95	$510.90