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	$32.82	3.223%	$33.8778	$33.88	$33.90	$33.90
Purchase #2	$179.72	5.751%	$190.0557	$190.06	$190.05	$190.10
Purchase #3	$238.89	10.291%	$263.4742	$263.47	$263.45	$263.50
Purchase #4	$226.98	4.638%	$237.5073	$237.51	$237.50	$237.50
Purchase #5	$173.59	7.864%	$187.2411	$187.24	$187.25	$187.20
Purchase #6	$139.47	13.555%	$158.3752	$158.38	$158.40	$158.40
Purchase #7	$222.84	13.116%	$252.0677	$252.07	$252.05	$252.10
7 purchase totals =	$1,214.31		$1,322.5990	$1,322.61	$1,322.60	$1,322.70