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	$10.54	9.142%	$11.5036	$11.50	$11.50	$11.50
Purchase #2	$59.53	6.737%	$63.5405	$63.54	$63.55	$63.50
Purchase #3	$65.38	11.411%	$72.8405	$72.84	$72.85	$72.80
Purchase #4	$9.53	13.829%	$10.8479	$10.85	$10.85	$10.80
Purchase #5	$50.42	4.620%	$52.7494	$52.75	$52.75	$52.70
Purchase #6	$106.33	10.546%	$117.5436	$117.54	$117.55	$117.50
Purchase #7	$190.73	5.295%	$200.8292	$200.83	$200.85	$200.80
7 purchase totals =	$492.46		$529.8547	$529.85	$529.90	$529.60