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	$124.36	13.593%	$141.2643	$141.26	$141.25	$141.30
Purchase #2	$133.57	13.630%	$151.7756	$151.78	$151.80	$151.80
Purchase #3	$78.34	6.274%	$83.2551	$83.26	$83.25	$83.30
Purchase #4	$11.70	8.560%	$12.7015	$12.70	$12.70	$12.70
Purchase #5	$95.67	3.622%	$99.1352	$99.14	$99.15	$99.10
Purchase #6	$229.46	4.517%	$239.8247	$239.82	$239.80	$239.80
Purchase #7	$100.59	3.284%	$103.8934	$103.89	$103.90	$103.90
7 purchase totals =	$773.69		$831.8498	$831.85	$831.85	$831.90