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	$18.56	12.340%	$20.8503	$20.85	$20.85	$20.90
Purchase #2	$38.29	3.847%	$39.763	$39.76	$39.75	$39.80
Purchase #3	$35.81	8.355%	$38.8019	$38.80	$38.80	$38.80
Purchase #4	$100.64	3.286%	$103.947	$103.95	$103.95	$103.90
Purchase #5	$168.64	4.585%	$176.3721	$176.37	$176.35	$176.40
Purchase #6	$29.71	9.756%	$32.6085	$32.61	$32.60	$32.60
Purchase #7	$158.64	5.623%	$167.5603	$167.56	$167.55	$167.60
7 purchase totals =	$550.29		$579.9031	$579.90	$579.85	$580.00