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	$66.88	4.725%	$70.0401	$70.04	$70.05	$70.00
Purchase #2	$59.71	5.473%	$62.9779	$62.98	$63.00	$63.00
Purchase #3	$39.66	12.386%	$44.5723	$44.57	$44.55	$44.60
Purchase #4	$126.80	13.275%	$143.6327	$143.63	$143.65	$143.60
Purchase #5	$98.41	7.239%	$105.5339	$105.53	$105.55	$105.50
Purchase #6	$170.46	10.827%	$188.9157	$188.92	$188.90	$188.90
Purchase #7	$160.58	8.249%	$173.8262	$173.83	$173.85	$173.80
7 purchase totals =	$722.50		$789.4988	$789.50	$789.55	$789.40