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	$242.53	8.320%	$262.7085	$262.71	$262.70	$262.70
Purchase #2	$37.47	13.677%	$42.5948	$42.59	$42.60	$42.60
Purchase #3	$221.80	12.499%	$249.5228	$249.52	$249.50	$249.50
Purchase #4	$210.78	8.479%	$228.652	$228.65	$228.65	$228.70
Purchase #5	$132.92	4.354%	$138.7073	$138.71	$138.70	$138.70
Purchase #6	$33.67	12.353%	$37.8293	$37.83	$37.85	$37.80
Purchase #7	$150.59	13.479%	$170.888	$170.89	$170.90	$170.90
7 purchase totals =	$1,029.76		$1,130.9027	$1,130.90	$1,130.90	$1,130.90