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	$40.78	3.399%	$42.1661	$42.17	$42.15	$42.20
Purchase #2	$16.52	13.736%	$18.7892	$18.79	$18.80	$18.80
Purchase #3	$63.82	6.445%	$67.9332	$67.93	$67.95	$67.90
Purchase #4	$240.28	8.533%	$260.7831	$260.78	$260.80	$260.80
Purchase #5	$14.81	6.810%	$15.8186	$15.82	$15.80	$15.80
Purchase #6	$73.81	13.232%	$83.5765	$83.58	$83.60	$83.60
Purchase #7	$22.42	13.747%	$25.5021	$25.50	$25.50	$25.50
7 purchase totals =	$472.44		$514.5688	$514.57	$514.60	$514.60