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	$160.59	3.858%	$166.7856	$166.79	$166.80	$166.80
Purchase #2	$28.37	10.793%	$31.432	$31.43	$31.45	$31.40
Purchase #3	$140.89	12.617%	$158.6661	$158.67	$158.65	$158.70
Purchase #4	$11.99	7.542%	$12.8943	$12.89	$12.90	$12.90
Purchase #5	$101.27	9.126%	$110.5119	$110.51	$110.50	$110.50
Purchase #6	$89.89	13.207%	$101.7618	$101.76	$101.75	$101.80
Purchase #7	$119.78	4.228%	$124.8443	$124.84	$124.85	$124.80
7 purchase totals =	$652.78		$706.8960	$706.89	$706.90	$706.90