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	$38.52	11.423%	$42.9201	$42.92	$42.90	$42.90
Purchase #2	$47.40	10.768%	$52.504	$52.50	$52.50	$52.50
Purchase #3	$224.48	6.732%	$239.592	$239.59	$239.60	$239.60
Purchase #4	$119.69	3.654%	$124.0635	$124.06	$124.05	$124.10
Purchase #5	$58.89	11.190%	$65.4798	$65.48	$65.50	$65.50
Purchase #6	$7.40	5.575%	$7.8126	$7.81	$7.80	$7.80
Purchase #7	$42.53	3.367%	$43.962	$43.96	$43.95	$44.00
7 purchase totals =	$538.91		$576.3340	$576.32	$576.30	$576.40