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	$235.43	13.207%	$266.5232	$266.52	$266.50	$266.50
Purchase #2	$242.71	9.159%	$264.9398	$264.94	$264.95	$264.90
Purchase #3	$172.94	7.481%	$185.8776	$185.88	$185.90	$185.90
Purchase #4	$169.69	12.509%	$190.9165	$190.92	$190.90	$190.90
Purchase #5	$153.95	8.422%	$166.9157	$166.92	$166.90	$166.90
Purchase #6	$63.45	13.605%	$72.0824	$72.08	$72.10	$72.10
Purchase #7	$250.62	10.707%	$277.4539	$277.45	$277.45	$277.50
7 purchase totals =	$1,288.79		$1,424.7091	$1,424.71	$1,424.70	$1,424.70