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	$60.83	3.239%	$62.8003	$62.80	$62.80	$62.80
Purchase #2	$65.81	5.665%	$69.5381	$69.54	$69.55	$69.50
Purchase #3	$32.71	9.829%	$35.9251	$35.93	$35.95	$35.90
Purchase #4	$76.41	5.709%	$80.7722	$80.77	$80.75	$80.80
Purchase #5	$249.37	9.268%	$272.4816	$272.48	$272.50	$272.50
Purchase #6	$66.89	3.635%	$69.3215	$69.32	$69.30	$69.30
Purchase #7	$32.87	13.571%	$37.3308	$37.33	$37.35	$37.30
7 purchase totals =	$584.89		$628.1696	$628.17	$628.20	$628.10