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	$50.56	12.547%	$56.9038	$56.90	$56.90	$56.90
Purchase #2	$248.52	4.764%	$260.3595	$260.36	$260.35	$260.40
Purchase #3	$205.75	10.605%	$227.5698	$227.57	$227.55	$227.60
Purchase #4	$118.89	3.480%	$123.0274	$123.03	$123.05	$123.00
Purchase #5	$17.45	7.454%	$18.7507	$18.75	$18.75	$18.80
Purchase #6	$94.31	8.388%	$102.2207	$102.22	$102.20	$102.20
Purchase #7	$189.52	13.189%	$214.5158	$214.52	$214.50	$214.50
7 purchase totals =	$925.00		$1,003.3477	$1,003.35	$1,003.30	$1,003.40