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	$31.51	4.169%	$32.8237	$32.82	$32.80	$32.80
Purchase #2	$122.98	7.162%	$131.7878	$131.79	$131.80	$131.80
Purchase #3	$231.50	12.392%	$260.1875	$260.19	$260.20	$260.20
Purchase #4	$133.53	3.784%	$138.5828	$138.58	$138.60	$138.60
Purchase #5	$246.89	13.352%	$279.8548	$279.85	$279.85	$279.90
Purchase #6	$73.61	13.584%	$83.6092	$83.61	$83.60	$83.60
Purchase #7	$220.52	8.559%	$239.3943	$239.39	$239.40	$239.40
7 purchase totals =	$1,060.54		$1,166.2401	$1,166.23	$1,166.25	$1,166.30