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	$170.78	8.636%	$185.5286	$185.53	$185.55	$185.50
Purchase #2	$128.54	10.257%	$141.7243	$141.72	$141.70	$141.70
Purchase #3	$77.53	10.284%	$85.5032	$85.50	$85.50	$85.50
Purchase #4	$215.27	6.297%	$228.8256	$228.83	$228.85	$228.80
Purchase #5	$63.81	6.485%	$67.9481	$67.95	$67.95	$67.90
Purchase #6	$60.75	9.600%	$66.582	$66.58	$66.60	$66.60
Purchase #7	$86.93	7.661%	$93.5897	$93.59	$93.60	$93.60
7 purchase totals =	$803.61		$869.7015	$869.70	$869.75	$869.60