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	$55.93	8.139%	$60.4821	$60.48	$60.50	$60.50
Purchase #2	$141.47	12.103%	$158.5921	$158.59	$158.60	$158.60
Purchase #3	$114.98	7.444%	$123.5391	$123.54	$123.55	$123.50
Purchase #4	$123.99	10.538%	$137.0561	$137.06	$137.05	$137.10
Purchase #5	$132.43	9.397%	$144.8744	$144.87	$144.85	$144.90
Purchase #6	$221.89	12.392%	$249.3866	$249.39	$249.40	$249.40
Purchase #7	$114.32	9.193%	$124.8294	$124.83	$124.85	$124.80
7 purchase totals =	$905.01		$998.7598	$998.76	$998.80	$998.80