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	$159.31	8.528%	$172.896	$172.90	$172.90	$172.90
Purchase #2	$29.70	5.475%	$31.3261	$31.33	$31.35	$31.30
Purchase #3	$19.59	6.795%	$20.9211	$20.92	$20.90	$20.90
Purchase #4	$38.48	6.307%	$40.9069	$40.91	$40.90	$40.90
Purchase #5	$213.77	12.628%	$240.7649	$240.76	$240.75	$240.80
Purchase #6	$17.82	7.131%	$19.0907	$19.09	$19.10	$19.10
Purchase #7	$155.82	5.629%	$164.5911	$164.59	$164.60	$164.60
7 purchase totals =	$634.49		$690.4968	$690.50	$690.50	$690.50