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	$80.53	10.610%	$89.0742	$89.07	$89.05	$89.10
Purchase #2	$50.52	12.778%	$56.9754	$56.98	$57.00	$57.00
Purchase #3	$119.64	3.300%	$123.5881	$123.59	$123.60	$123.60
Purchase #4	$135.88	7.511%	$146.0859	$146.09	$146.10	$146.10
Purchase #5	$250.25	9.672%	$274.4542	$274.45	$274.45	$274.50
Purchase #6	$244.34	4.201%	$254.6047	$254.60	$254.60	$254.60
Purchase #7	$29.75	13.262%	$33.6954	$33.70	$33.70	$33.70
7 purchase totals =	$910.91		$978.4779	$978.48	$978.50	$978.60