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	$71.53	9.863%	$78.585	$78.59	$78.60	$78.60
Purchase #2	$124.72	11.177%	$138.66	$138.66	$138.65	$138.70
Purchase #3	$59.68	4.618%	$62.436	$62.44	$62.45	$62.40
Purchase #4	$131.34	13.847%	$149.5266	$149.53	$149.55	$149.50
Purchase #5	$96.60	8.492%	$104.8033	$104.80	$104.80	$104.80
Purchase #6	$62.75	11.337%	$69.864	$69.86	$69.85	$69.90
Purchase #7	$6.52	7.731%	$7.0241	$7.02	$7.00	$7.00
7 purchase totals =	$553.14		$610.8990	$610.90	$610.90	$610.90