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	$128.75	9.348%	$140.7856	$140.79	$140.80	$140.80
Purchase #2	$48.29	13.523%	$54.8203	$54.82	$54.80	$54.80
Purchase #3	$179.95	5.491%	$189.8311	$189.83	$189.85	$189.80
Purchase #4	$224.65	9.502%	$245.9962	$246.00	$246.00	$246.00
Purchase #5	$63.90	13.793%	$72.7137	$72.71	$72.70	$72.70
Purchase #6	$157.79	5.495%	$166.4606	$166.46	$166.45	$166.50
Purchase #7	$56.99	10.364%	$62.8964	$62.90	$62.90	$62.90
7 purchase totals =	$860.32		$933.5039	$933.51	$933.50	$933.50