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	$65.37	8.447%	$70.8918	$70.89	$70.90	$70.90
Purchase #2	$65.80	10.683%	$72.8294	$72.83	$72.85	$72.80
Purchase #3	$137.92	4.162%	$143.6602	$143.66	$143.65	$143.70
Purchase #4	$140.45	13.841%	$159.8897	$159.89	$159.90	$159.90
Purchase #5	$195.50	9.421%	$213.9181	$213.92	$213.90	$213.90
Purchase #6	$58.44	3.681%	$60.5912	$60.59	$60.60	$60.60
Purchase #7	$43.72	12.868%	$49.3459	$49.35	$49.35	$49.30
7 purchase totals =	$707.20		$771.1263	$771.13	$771.15	$771.10