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	$156.27	10.149%	$172.1298	$172.13	$172.15	$172.10
Purchase #2	$192.37	12.111%	$215.6679	$215.67	$215.65	$215.70
Purchase #3	$93.39	11.454%	$104.0869	$104.09	$104.10	$104.10
Purchase #4	$16.79	8.703%	$18.2512	$18.25	$18.25	$18.30
Purchase #5	$175.43	5.779%	$185.5681	$185.57	$185.55	$185.60
Purchase #6	$135.51	6.664%	$144.5404	$144.54	$144.55	$144.50
Purchase #7	$62.79	4.491%	$65.6099	$65.61	$65.60	$65.60
7 purchase totals =	$832.55		$905.8542	$905.86	$905.85	$905.90