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	$120.59	10.742%	$133.5438	$133.54	$133.55	$133.50
Purchase #2	$89.28	12.196%	$100.1686	$100.17	$100.15	$100.20
Purchase #3	$154.48	11.798%	$172.7056	$172.71	$172.70	$172.70
Purchase #4	$101.96	8.347%	$110.4706	$110.47	$110.45	$110.50
Purchase #5	$44.77	8.526%	$48.5871	$48.59	$48.60	$48.60
Purchase #6	$154.80	11.769%	$173.0184	$173.02	$173.00	$173.00
Purchase #7	$123.84	3.676%	$128.3924	$128.39	$128.40	$128.40
7 purchase totals =	$789.72		$866.8865	$866.89	$866.85	$866.90