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	$53.57	3.132%	$55.2478	$55.25	$55.25	$55.20
Purchase #2	$174.46	12.364%	$196.0302	$196.03	$196.05	$196.00
Purchase #3	$105.60	10.857%	$117.065	$117.07	$117.05	$117.10
Purchase #4	$172.48	9.259%	$188.4499	$188.45	$188.45	$188.40
Purchase #5	$162.78	3.636%	$168.6987	$168.70	$168.70	$168.70
Purchase #6	$37.85	8.384%	$41.0233	$41.02	$41.00	$41.00
Purchase #7	$203.75	4.720%	$213.367	$213.37	$213.35	$213.40
7 purchase totals =	$910.49		$979.8819	$979.89	$979.85	$979.80