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	$59.56	9.122%	$64.9931	$64.99	$65.00	$65.00
Purchase #2	$21.61	11.447%	$24.0837	$24.08	$24.10	$24.10
Purchase #3	$87.45	3.225%	$90.2703	$90.27	$90.25	$90.30
Purchase #4	$59.41	3.505%	$61.4923	$61.49	$61.50	$61.50
Purchase #5	$80.80	3.777%	$83.8518	$83.85	$83.85	$83.90
Purchase #6	$94.83	5.210%	$99.7706	$99.77	$99.75	$99.80
Purchase #7	$202.41	4.866%	$212.2593	$212.26	$212.25	$212.30
7 purchase totals =	$606.07		$636.7211	$636.71	$636.70	$636.90