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	$15.37	3.516%	$15.9104	$15.91	$15.90	$15.90
Purchase #2	$104.60	11.186%	$116.3006	$116.30	$116.30	$116.30
Purchase #3	$58.87	5.858%	$62.3186	$62.32	$62.30	$62.30
Purchase #4	$154.52	13.804%	$175.8499	$175.85	$175.85	$175.80
Purchase #5	$210.81	10.652%	$233.2655	$233.27	$233.25	$233.30
Purchase #6	$9.33	11.240%	$10.3787	$10.38	$10.40	$10.40
Purchase #7	$86.87	6.566%	$92.5739	$92.57	$92.55	$92.60
7 purchase totals =	$640.37		$706.5976	$706.60	$706.55	$706.60