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	$84.53	6.787%	$90.2671	$90.27	$90.25	$90.30
Purchase #2	$189.27	9.105%	$206.503	$206.50	$206.50	$206.50
Purchase #3	$183.48	11.455%	$204.4976	$204.50	$204.50	$204.50
Purchase #4	$25.86	12.208%	$29.017	$29.02	$29.00	$29.00
Purchase #5	$175.93	4.280%	$183.4598	$183.46	$183.45	$183.50
Purchase #6	$204.42	10.347%	$225.5713	$225.57	$225.55	$225.60
Purchase #7	$128.35	11.149%	$142.6597	$142.66	$142.65	$142.70
7 purchase totals =	$991.84		$1,081.9755	$1,081.98	$1,081.90	$1,082.10