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	$76.99	5.621%	$81.3176	$81.32	$81.30	$81.30
Purchase #2	$108.73	10.228%	$119.8509	$119.85	$119.85	$119.90
Purchase #3	$72.39	8.559%	$78.5859	$78.59	$78.60	$78.60
Purchase #4	$109.42	7.636%	$117.7753	$117.78	$117.80	$117.80
Purchase #5	$29.90	10.619%	$33.0751	$33.08	$33.10	$33.10
Purchase #6	$68.52	7.668%	$73.7741	$73.77	$73.75	$73.80
Purchase #7	$158.57	8.701%	$172.3672	$172.37	$172.35	$172.40
7 purchase totals =	$624.52		$676.7461	$676.76	$676.75	$676.90