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	$128.66	6.725%	$137.3124	$137.31	$137.30	$137.30
Purchase #2	$172.88	5.192%	$181.8559	$181.86	$181.85	$181.90
Purchase #3	$120.76	10.341%	$133.2478	$133.25	$133.25	$133.20
Purchase #4	$17.31	8.506%	$18.7824	$18.78	$18.80	$18.80
Purchase #5	$10.75	4.221%	$11.2038	$11.20	$11.20	$11.20
Purchase #6	$241.38	7.530%	$259.5559	$259.56	$259.55	$259.60
Purchase #7	$237.49	7.735%	$255.8599	$255.86	$255.85	$255.90
7 purchase totals =	$929.23		$997.8181	$997.82	$997.80	$997.90