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	$139.92	10.846%	$155.0957	$155.10	$155.10	$155.10
Purchase #2	$64.94	5.482%	$68.5	$68.50	$68.50	$68.50
Purchase #3	$94.75	4.513%	$99.0261	$99.03	$99.05	$99.00
Purchase #4	$69.85	11.777%	$78.0762	$78.08	$78.10	$78.10
Purchase #5	$13.50	8.171%	$14.6031	$14.60	$14.60	$14.60
Purchase #6	$74.93	4.597%	$78.3745	$78.37	$78.35	$78.40
Purchase #7	$77.70	12.385%	$87.3231	$87.32	$87.30	$87.30
7 purchase totals =	$535.59		$580.9987	$581.00	$581.00	$581.00