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	$13.66	9.628%	$14.9752	$14.98	$15.00	$15.00
Purchase #2	$85.50	5.757%	$90.4222	$90.42	$90.40	$90.40
Purchase #3	$89.99	4.672%	$94.1943	$94.19	$94.20	$94.20
Purchase #4	$194.71	4.850%	$204.1534	$204.15	$204.15	$204.20
Purchase #5	$125.98	4.481%	$131.6252	$131.63	$131.65	$131.60
Purchase #6	$94.41	6.714%	$100.7487	$100.75	$100.75	$100.70
Purchase #7	$78.33	6.410%	$83.351	$83.35	$83.35	$83.40
7 purchase totals =	$682.58		$719.4700	$719.47	$719.50	$719.50