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	$94.47	6.802%	$100.8958	$100.90	$100.90	$100.90
Purchase #2	$128.42	11.557%	$143.2615	$143.26	$143.25	$143.30
Purchase #3	$138.54	4.417%	$144.6593	$144.66	$144.65	$144.70
Purchase #4	$123.97	13.367%	$140.5411	$140.54	$140.55	$140.50
Purchase #5	$49.81	7.626%	$53.6085	$53.61	$53.60	$53.60
Purchase #6	$165.69	4.113%	$172.5048	$172.50	$172.50	$172.50
Purchase #7	$120.67	6.135%	$128.0731	$128.07	$128.05	$128.10
7 purchase totals =	$821.57		$883.5441	$883.54	$883.50	$883.60