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	$44.85	10.185%	$49.418	$49.42	$49.40	$49.40
Purchase #2	$166.78	5.300%	$175.6193	$175.62	$175.60	$175.60
Purchase #3	$161.58	8.559%	$175.4096	$175.41	$175.40	$175.40
Purchase #4	$58.76	5.229%	$61.8326	$61.83	$61.85	$61.80
Purchase #5	$206.78	4.192%	$215.4482	$215.45	$215.45	$215.40
Purchase #6	$158.76	10.442%	$175.3377	$175.34	$175.35	$175.30
Purchase #7	$45.59	6.431%	$48.5219	$48.52	$48.50	$48.50
7 purchase totals =	$843.10		$901.5873	$901.59	$901.55	$901.40