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	$29.40	9.160%	$32.093	$32.09	$32.10	$32.10
Purchase #2	$196.71	7.490%	$211.4436	$211.44	$211.45	$211.40
Purchase #3	$17.42	5.262%	$18.3366	$18.34	$18.35	$18.30
Purchase #4	$152.61	3.246%	$157.5637	$157.56	$157.55	$157.60
Purchase #5	$59.75	11.464%	$66.5997	$66.60	$66.60	$66.60
Purchase #6	$91.26	9.606%	$100.0264	$100.03	$100.05	$100.00
Purchase #7	$78.57	12.341%	$88.2663	$88.27	$88.25	$88.30
7 purchase totals =	$625.72		$674.3293	$674.33	$674.35	$674.30