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	$54.29	4.227%	$56.5848	$56.58	$56.60	$56.60
Purchase #2	$175.70	11.659%	$196.1849	$196.18	$196.20	$196.20
Purchase #3	$62.36	7.602%	$67.1006	$67.10	$67.10	$67.10
Purchase #4	$59.94	12.158%	$67.2275	$67.23	$67.25	$67.20
Purchase #5	$183.29	9.404%	$200.5266	$200.53	$200.55	$200.50
Purchase #6	$234.61	10.627%	$259.542	$259.54	$259.55	$259.50
Purchase #7	$20.99	8.788%	$22.8346	$22.83	$22.85	$22.80
7 purchase totals =	$791.18		$870.0010	$869.99	$870.10	$869.90