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	$59.74	10.256%	$65.8669	$65.87	$65.85	$65.90
Purchase #2	$122.93	8.687%	$133.6089	$133.61	$133.60	$133.60
Purchase #3	$18.31	3.664%	$18.9809	$18.98	$19.00	$19.00
Purchase #4	$77.28	6.333%	$82.1741	$82.17	$82.15	$82.20
Purchase #5	$134.68	8.309%	$145.8706	$145.87	$145.85	$145.90
Purchase #6	$28.52	10.401%	$31.4864	$31.49	$31.50	$31.50
Purchase #7	$76.29	9.837%	$83.7946	$83.79	$83.80	$83.80
7 purchase totals =	$517.75		$561.7824	$561.78	$561.75	$561.90