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	$12.86	5.379%	$13.5517	$13.55	$13.55	$13.60
Purchase #2	$48.32	7.244%	$51.8203	$51.82	$51.80	$51.80
Purchase #3	$163.42	4.346%	$170.5222	$170.52	$170.50	$170.50
Purchase #4	$95.38	5.724%	$100.8396	$100.84	$100.85	$100.80
Purchase #5	$101.99	10.532%	$112.7316	$112.73	$112.75	$112.70
Purchase #6	$195.77	12.321%	$219.8908	$219.89	$219.90	$219.90
Purchase #7	$140.94	3.611%	$146.0293	$146.03	$146.05	$146.00
7 purchase totals =	$758.68		$815.3855	$815.38	$815.40	$815.30