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	$92.65	8.488%	$100.5141	$100.51	$100.50	$100.50
Purchase #2	$198.48	13.667%	$225.6063	$225.61	$225.60	$225.60
Purchase #3	$235.80	6.712%	$251.6269	$251.63	$251.65	$251.60
Purchase #4	$78.62	5.849%	$83.2185	$83.22	$83.20	$83.20
Purchase #5	$122.31	11.659%	$136.5701	$136.57	$136.55	$136.60
Purchase #6	$245.59	11.699%	$274.3216	$274.32	$274.30	$274.30
Purchase #7	$90.30	10.166%	$99.4799	$99.48	$99.50	$99.50
7 purchase totals =	$1,063.75		$1,171.3374	$1,171.34	$1,171.30	$1,171.30