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	$206.87	8.714%	$224.8967	$224.90	$224.90	$224.90
Purchase #2	$55.86	3.709%	$57.9318	$57.93	$57.95	$57.90
Purchase #3	$38.39	12.620%	$43.2348	$43.23	$43.25	$43.20
Purchase #4	$28.70	4.158%	$29.8933	$29.89	$29.90	$29.90
Purchase #5	$35.57	4.312%	$37.1038	$37.10	$37.10	$37.10
Purchase #6	$14.86	4.156%	$15.4776	$15.48	$15.50	$15.50
Purchase #7	$129.98	10.382%	$143.4745	$143.47	$143.45	$143.50
7 purchase totals =	$510.23		$552.0125	$552.00	$552.05	$552.00