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	$211.93	10.807%	$234.8333	$234.83	$234.85	$234.80
Purchase #2	$38.77	5.407%	$40.8663	$40.87	$40.85	$40.90
Purchase #3	$247.83	11.292%	$275.815	$275.82	$275.80	$275.80
Purchase #4	$17.65	7.590%	$18.9896	$18.99	$19.00	$19.00
Purchase #5	$235.62	12.496%	$265.0631	$265.06	$265.05	$265.10
Purchase #6	$61.39	6.630%	$65.4602	$65.46	$65.45	$65.50
Purchase #7	$56.98	4.465%	$59.5242	$59.52	$59.50	$59.50
7 purchase totals =	$870.17		$960.5517	$960.55	$960.50	$960.60