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	$89.32	3.465%	$92.4149	$92.41	$92.40	$92.40
Purchase #2	$21.72	12.439%	$24.4218	$24.42	$24.40	$24.40
Purchase #3	$56.99	8.447%	$61.8039	$61.80	$61.80	$61.80
Purchase #4	$42.71	13.800%	$48.604	$48.60	$48.60	$48.60
Purchase #5	$138.57	10.330%	$152.8843	$152.88	$152.90	$152.90
Purchase #6	$6.74	7.643%	$7.2551	$7.26	$7.25	$7.30
Purchase #7	$161.61	5.491%	$170.484	$170.48	$170.50	$170.50
7 purchase totals =	$517.66		$557.8680	$557.85	$557.85	$557.90