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	$161.78	4.183%	$168.5473	$168.55	$168.55	$168.50
Purchase #2	$92.57	12.636%	$104.2671	$104.27	$104.25	$104.30
Purchase #3	$103.74	8.227%	$112.2747	$112.27	$112.25	$112.30
Purchase #4	$12.64	5.520%	$13.3377	$13.34	$13.35	$13.30
Purchase #5	$16.38	5.204%	$17.2324	$17.23	$17.25	$17.20
Purchase #6	$210.42	12.106%	$235.8934	$235.89	$235.90	$235.90
Purchase #7	$10.25	12.125%	$11.4928	$11.49	$11.50	$11.50
7 purchase totals =	$607.78		$663.0454	$663.04	$663.05	$663.00