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	$118.85	10.607%	$131.4564	$131.46	$131.45	$131.50
Purchase #2	$23.76	6.562%	$25.3191	$25.32	$25.30	$25.30
Purchase #3	$48.56	5.553%	$51.2565	$51.26	$51.25	$51.30
Purchase #4	$54.63	9.547%	$59.8455	$59.85	$59.85	$59.80
Purchase #5	$171.90	10.256%	$189.5301	$189.53	$189.55	$189.50
Purchase #6	$8.49	7.763%	$9.1491	$9.15	$9.15	$9.10
Purchase #7	$159.26	8.652%	$173.0392	$173.04	$173.05	$173.00
7 purchase totals =	$585.45		$639.5959	$639.61	$639.60	$639.50