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	$49.85	4.178%	$51.9327	$51.93	$51.95	$51.90
Purchase #2	$105.36	7.335%	$113.0882	$113.09	$113.10	$113.10
Purchase #3	$48.46	13.123%	$54.8194	$54.82	$54.80	$54.80
Purchase #4	$57.97	8.395%	$62.8366	$62.84	$62.85	$62.80
Purchase #5	$38.59	4.703%	$40.4049	$40.40	$40.40	$40.40
Purchase #6	$104.83	9.366%	$114.6484	$114.65	$114.65	$114.60
Purchase #7	$212.31	5.208%	$223.3671	$223.37	$223.35	$223.40
7 purchase totals =	$617.37		$661.0973	$661.10	$661.10	$661.00