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	$138.59	3.177%	$142.993	$142.99	$143.00	$143.00
Purchase #2	$53.73	5.376%	$56.6185	$56.62	$56.60	$56.60
Purchase #3	$208.85	8.161%	$225.8942	$225.89	$225.90	$225.90
Purchase #4	$40.48	5.517%	$42.7133	$42.71	$42.70	$42.70
Purchase #5	$89.89	3.485%	$93.0227	$93.02	$93.00	$93.00
Purchase #6	$127.87	10.390%	$141.1557	$141.16	$141.15	$141.20
Purchase #7	$62.96	5.660%	$66.5235	$66.52	$66.50	$66.50
7 purchase totals =	$722.37		$768.9209	$768.91	$768.85	$768.90