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	$35.42	4.763%	$37.1071	$37.11	$37.10	$37.10
Purchase #2	$58.80	12.845%	$66.3529	$66.35	$66.35	$66.40
Purchase #3	$100.90	10.259%	$111.2513	$111.25	$111.25	$111.30
Purchase #4	$128.61	13.110%	$145.4708	$145.47	$145.45	$145.50
Purchase #5	$76.90	13.555%	$87.3238	$87.32	$87.30	$87.30
Purchase #6	$15.89	4.363%	$16.5833	$16.58	$16.60	$16.60
Purchase #7	$58.99	3.872%	$61.2741	$61.27	$61.25	$61.30
7 purchase totals =	$475.51		$525.3633	$525.35	$525.30	$525.50