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	$222.36	12.147%	$249.3701	$249.37	$249.35	$249.40
Purchase #2	$158.75	8.735%	$172.6168	$172.62	$172.60	$172.60
Purchase #3	$46.25	11.382%	$51.5142	$51.51	$51.50	$51.50
Purchase #4	$62.53	8.483%	$67.8344	$67.83	$67.85	$67.80
Purchase #5	$38.80	6.578%	$41.3523	$41.35	$41.35	$41.40
Purchase #6	$191.34	6.365%	$203.5188	$203.52	$203.50	$203.50
Purchase #7	$158.86	8.191%	$171.8722	$171.87	$171.85	$171.90
7 purchase totals =	$878.89		$958.0788	$958.07	$958.00	$958.10