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	$15.69	5.290%	$16.52	$16.52	$16.50	$16.50
Purchase #2	$106.77	4.547%	$111.6248	$111.62	$111.60	$111.60
Purchase #3	$179.81	11.660%	$200.7758	$200.78	$200.80	$200.80
Purchase #4	$249.52	12.394%	$280.4455	$280.45	$280.45	$280.40
Purchase #5	$63.92	5.731%	$67.5833	$67.58	$67.60	$67.60
Purchase #6	$78.91	6.301%	$83.8821	$83.88	$83.90	$83.90
Purchase #7	$118.80	3.548%	$123.015	$123.02	$123.00	$123.00
7 purchase totals =	$813.42		$883.8465	$883.85	$883.85	$883.80