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	$28.76	8.108%	$31.0919	$31.09	$31.10	$31.10
Purchase #2	$133.34	4.815%	$139.7603	$139.76	$139.75	$139.80
Purchase #3	$154.88	11.360%	$172.4744	$172.47	$172.45	$172.50
Purchase #4	$112.79	13.160%	$127.6332	$127.63	$127.65	$127.60
Purchase #5	$60.76	7.845%	$65.5266	$65.53	$65.55	$65.50
Purchase #6	$63.34	8.393%	$68.6561	$68.66	$68.65	$68.70
Purchase #7	$136.83	9.731%	$150.1449	$150.14	$150.15	$150.10
7 purchase totals =	$690.70		$755.2874	$755.28	$755.30	$755.30