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	$55.63	10.602%	$61.5279	$61.53	$61.55	$61.50
Purchase #2	$145.96	8.856%	$158.8862	$158.89	$158.90	$158.90
Purchase #3	$12.83	7.348%	$13.7727	$13.77	$13.75	$13.80
Purchase #4	$51.97	8.872%	$56.5808	$56.58	$56.60	$56.60
Purchase #5	$21.97	8.203%	$23.7722	$23.77	$23.75	$23.80
Purchase #6	$89.97	9.454%	$98.4758	$98.48	$98.50	$98.50
Purchase #7	$71.35	10.461%	$78.8139	$78.81	$78.80	$78.80
7 purchase totals =	$449.68		$491.8295	$491.83	$491.85	$491.90