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	$78.93	3.752%	$81.8915	$81.89	$81.90	$81.90
Purchase #2	$66.53	7.364%	$71.4293	$71.43	$71.45	$71.40
Purchase #3	$134.32	8.294%	$145.4605	$145.46	$145.45	$145.50
Purchase #4	$162.27	4.588%	$169.7149	$169.71	$169.70	$169.70
Purchase #5	$199.66	4.632%	$208.9083	$208.91	$208.90	$208.90
Purchase #6	$23.49	3.673%	$24.3528	$24.35	$24.35	$24.40
Purchase #7	$48.64	4.518%	$50.8376	$50.84	$50.85	$50.80
7 purchase totals =	$713.84		$752.5949	$752.59	$752.60	$752.60