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	$36.68	10.152%	$40.4038	$40.40	$40.40	$40.40
Purchase #2	$36.66	7.271%	$39.3255	$39.33	$39.35	$39.30
Purchase #3	$79.54	13.168%	$90.0138	$90.01	$90.00	$90.00
Purchase #4	$75.50	10.477%	$83.4101	$83.41	$83.40	$83.40
Purchase #5	$59.85	5.686%	$63.2531	$63.25	$63.25	$63.30
Purchase #6	$146.94	11.527%	$163.8778	$163.88	$163.90	$163.90
Purchase #7	$35.81	7.317%	$38.4302	$38.43	$38.45	$38.40
7 purchase totals =	$470.98		$518.7143	$518.71	$518.75	$518.70