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	$53.34	11.504%	$59.4762	$59.48	$59.50	$59.50
Purchase #2	$79.45	7.339%	$85.2808	$85.28	$85.30	$85.30
Purchase #3	$76.72	13.400%	$87.0005	$87.00	$87.00	$87.00
Purchase #4	$13.38	11.220%	$14.8812	$14.88	$14.90	$14.90
Purchase #5	$99.79	8.177%	$107.9498	$107.95	$107.95	$107.90
Purchase #6	$115.72	5.570%	$122.1656	$122.17	$122.15	$122.20
Purchase #7	$94.49	11.664%	$105.5113	$105.51	$105.50	$105.50
7 purchase totals =	$532.89		$582.2654	$582.27	$582.30	$582.30