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	$103.70	7.429%	$111.4039	$111.40	$111.40	$111.40
Purchase #2	$50.86	3.278%	$52.5272	$52.53	$52.55	$52.50
Purchase #3	$55.28	7.853%	$59.6211	$59.62	$59.60	$59.60
Purchase #4	$154.62	6.649%	$164.9007	$164.90	$164.90	$164.90
Purchase #5	$63.89	11.712%	$71.3728	$71.37	$71.35	$71.40
Purchase #6	$46.30	4.786%	$48.5159	$48.52	$48.50	$48.50
Purchase #7	$42.96	12.137%	$48.1741	$48.17	$48.15	$48.20
7 purchase totals =	$517.61		$556.5157	$556.51	$556.45	$556.50