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	$136.47	6.598%	$145.4743	$145.47	$145.45	$145.50
Purchase #2	$117.57	5.744%	$124.3232	$124.32	$124.30	$124.30
Purchase #3	$125.89	8.105%	$136.0934	$136.09	$136.10	$136.10
Purchase #4	$169.91	13.513%	$192.8699	$192.87	$192.85	$192.90
Purchase #5	$214.55	3.684%	$222.454	$222.45	$222.45	$222.50
Purchase #6	$94.67	10.606%	$104.7107	$104.71	$104.70	$104.70
Purchase #7	$140.79	13.870%	$160.3176	$160.32	$160.30	$160.30
7 purchase totals =	$999.85		$1,086.2431	$1,086.23	$1,086.15	$1,086.30