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	$17.97	3.442%	$18.5885	$18.59	$18.60	$18.60
Purchase #2	$92.47	8.690%	$100.5056	$100.51	$100.50	$100.50
Purchase #3	$185.88	11.415%	$207.0982	$207.10	$207.10	$207.10
Purchase #4	$94.58	6.111%	$100.3598	$100.36	$100.35	$100.40
Purchase #5	$199.45	7.383%	$214.1754	$214.18	$214.20	$214.20
Purchase #6	$52.53	12.141%	$58.9077	$58.91	$58.90	$58.90
Purchase #7	$24.93	10.126%	$27.4544	$27.45	$27.45	$27.50
7 purchase totals =	$667.81		$727.0896	$727.10	$727.10	$727.20