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	$143.93	8.304%	$155.8819	$155.88	$155.90	$155.90
Purchase #2	$103.34	8.555%	$112.1807	$112.18	$112.20	$112.20
Purchase #3	$190.70	11.611%	$212.8422	$212.84	$212.85	$212.80
Purchase #4	$20.82	5.247%	$21.9124	$21.91	$21.90	$21.90
Purchase #5	$97.41	3.571%	$100.8885	$100.89	$100.90	$100.90
Purchase #6	$85.74	10.840%	$95.0342	$95.03	$95.05	$95.00
Purchase #7	$57.59	5.227%	$60.6002	$60.60	$60.60	$60.60
7 purchase totals =	$699.53		$759.3401	$759.33	$759.40	$759.30