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	$66.55	11.455%	$74.1733	$74.17	$74.15	$74.20
Purchase #2	$78.59	10.208%	$86.6125	$86.61	$86.60	$86.60
Purchase #3	$204.99	5.321%	$215.8975	$215.90	$215.90	$215.90
Purchase #4	$112.26	11.350%	$125.0015	$125.00	$125.00	$125.00
Purchase #5	$113.85	8.796%	$123.8642	$123.86	$123.85	$123.90
Purchase #6	$143.41	6.324%	$152.4792	$152.48	$152.50	$152.50
Purchase #7	$54.89	12.677%	$61.8484	$61.85	$61.85	$61.80
7 purchase totals =	$774.54		$839.8766	$839.87	$839.85	$839.90