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	$126.56	10.440%	$139.7729	$139.77	$139.75	$139.80
Purchase #2	$125.74	9.313%	$137.4502	$137.45	$137.45	$137.50
Purchase #3	$18.78	9.829%	$20.6259	$20.63	$20.65	$20.60
Purchase #4	$248.30	5.339%	$261.5567	$261.56	$261.55	$261.60
Purchase #5	$227.97	6.730%	$243.3124	$243.31	$243.30	$243.30
Purchase #6	$136.82	3.726%	$141.9179	$141.92	$141.90	$141.90
Purchase #7	$19.66	3.278%	$20.3045	$20.30	$20.30	$20.30
7 purchase totals =	$903.83		$964.9405	$964.94	$964.90	$965.00