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	$100.71	10.496%	$111.2805	$111.28	$111.30	$111.30
Purchase #2	$46.66	9.315%	$51.0064	$51.01	$51.00	$51.00
Purchase #3	$123.45	6.742%	$131.773	$131.77	$131.75	$131.80
Purchase #4	$10.90	6.787%	$11.6398	$11.64	$11.65	$11.60
Purchase #5	$36.69	6.447%	$39.0554	$39.06	$39.05	$39.10
Purchase #6	$94.28	5.609%	$99.5682	$99.57	$99.55	$99.60
Purchase #7	$180.83	8.833%	$196.8027	$196.80	$196.80	$196.80
7 purchase totals =	$593.52		$641.1260	$641.13	$641.10	$641.20