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	$122.55	13.585%	$139.1984	$139.20	$139.20	$139.20
Purchase #2	$16.99	9.417%	$18.5899	$18.59	$18.60	$18.60
Purchase #3	$100.79	10.155%	$111.0252	$111.03	$111.05	$111.00
Purchase #4	$115.87	6.601%	$123.5186	$123.52	$123.50	$123.50
Purchase #5	$160.50	13.293%	$181.8353	$181.84	$181.85	$181.80
Purchase #6	$232.95	12.859%	$262.905	$262.91	$262.90	$262.90
Purchase #7	$35.72	10.411%	$39.4388	$39.44	$39.45	$39.40
7 purchase totals =	$785.37		$876.5112	$876.53	$876.55	$876.40