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	$11.97	12.231%	$13.4341	$13.43	$13.45	$13.40
Purchase #2	$138.78	11.236%	$154.3733	$154.37	$154.35	$154.40
Purchase #3	$75.74	4.173%	$78.9006	$78.90	$78.90	$78.90
Purchase #4	$95.78	8.346%	$103.7738	$103.77	$103.75	$103.80
Purchase #5	$56.56	12.446%	$63.5995	$63.60	$63.60	$63.60
Purchase #6	$200.43	3.837%	$208.1205	$208.12	$208.10	$208.10
Purchase #7	$129.64	9.576%	$142.0543	$142.05	$142.05	$142.10
7 purchase totals =	$708.90		$764.2561	$764.24	$764.20	$764.30