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	$185.60	11.678%	$207.2744	$207.27	$207.25	$207.30
Purchase #2	$65.25	8.461%	$70.7708	$70.77	$70.75	$70.80
Purchase #3	$88.85	12.396%	$99.8638	$99.86	$99.85	$99.90
Purchase #4	$204.62	6.678%	$218.2845	$218.28	$218.30	$218.30
Purchase #5	$92.80	3.206%	$95.7752	$95.78	$95.80	$95.80
Purchase #6	$97.37	5.215%	$102.4478	$102.45	$102.45	$102.40
Purchase #7	$100.90	3.548%	$104.4799	$104.48	$104.50	$104.50
7 purchase totals =	$835.39		$898.8964	$898.89	$898.90	$899.00