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	$36.47	5.504%	$38.4773	$38.48	$38.50	$38.50
Purchase #2	$37.59	3.720%	$38.9883	$38.99	$39.00	$39.00
Purchase #3	$200.46	11.603%	$223.7194	$223.72	$223.70	$223.70
Purchase #4	$85.49	5.726%	$90.3852	$90.39	$90.40	$90.40
Purchase #5	$217.33	7.166%	$232.9039	$232.90	$232.90	$232.90
Purchase #6	$104.65	7.403%	$112.3972	$112.40	$112.40	$112.40
Purchase #7	$106.78	10.262%	$117.7378	$117.74	$117.75	$117.70
7 purchase totals =	$788.77		$854.6091	$854.62	$854.65	$854.60