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	$13.59	10.553%	$15.0242	$15.02	$15.00	$15.00
Purchase #2	$134.51	6.800%	$143.6567	$143.66	$143.65	$143.70
Purchase #3	$76.77	9.114%	$83.7668	$83.77	$83.75	$83.80
Purchase #4	$228.71	12.166%	$256.5349	$256.53	$256.55	$256.50
Purchase #5	$130.92	9.425%	$143.2592	$143.26	$143.25	$143.30
Purchase #6	$120.78	8.857%	$131.4775	$131.48	$131.50	$131.50
Purchase #7	$144.91	3.593%	$150.1166	$150.12	$150.10	$150.10
7 purchase totals =	$850.19		$923.8359	$923.84	$923.80	$923.90