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	$76.56	5.274%	$80.5978	$80.60	$80.60	$80.60
Purchase #2	$184.65	3.852%	$191.7627	$191.76	$191.75	$191.80
Purchase #3	$154.76	9.707%	$169.7826	$169.78	$169.80	$169.80
Purchase #4	$29.32	8.721%	$31.877	$31.88	$31.90	$31.90
Purchase #5	$79.54	9.246%	$86.8943	$86.89	$86.90	$86.90
Purchase #6	$16.55	5.788%	$17.5079	$17.51	$17.50	$17.50
Purchase #7	$76.78	13.390%	$87.0608	$87.06	$87.05	$87.10
7 purchase totals =	$618.16		$665.4831	$665.48	$665.50	$665.60