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	$114.78	11.324%	$127.7777	$127.78	$127.80	$127.80
Purchase #2	$229.81	3.740%	$238.4049	$238.40	$238.40	$238.40
Purchase #3	$56.83	11.303%	$63.2535	$63.25	$63.25	$63.30
Purchase #4	$191.40	10.389%	$211.2845	$211.28	$211.30	$211.30
Purchase #5	$19.47	5.724%	$20.5845	$20.58	$20.60	$20.60
Purchase #6	$209.96	11.255%	$233.591	$233.59	$233.60	$233.60
Purchase #7	$44.81	8.737%	$48.725	$48.73	$48.75	$48.70
7 purchase totals =	$867.06		$943.6211	$943.61	$943.70	$943.70