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	$5.57	13.462%	$6.3198	$6.32	$6.30	$6.30
Purchase #2	$80.73	5.337%	$85.0386	$85.04	$85.05	$85.00
Purchase #3	$200.62	12.457%	$225.6112	$225.61	$225.60	$225.60
Purchase #4	$74.53	11.219%	$82.8915	$82.89	$82.90	$82.90
Purchase #5	$227.75	13.634%	$258.8014	$258.80	$258.80	$258.80
Purchase #6	$24.86	3.343%	$25.6911	$25.69	$25.70	$25.70
Purchase #7	$74.83	8.859%	$81.4592	$81.46	$81.45	$81.50
7 purchase totals =	$688.89		$765.8128	$765.81	$765.80	$765.80