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	$17.26	13.259%	$19.5485	$19.55	$19.55	$19.50
Purchase #2	$73.82	5.660%	$77.9982	$78.00	$78.00	$78.00
Purchase #3	$108.79	13.730%	$123.7269	$123.73	$123.75	$123.70
Purchase #4	$206.26	7.664%	$222.0678	$222.07	$222.05	$222.10
Purchase #5	$226.25	7.221%	$242.5875	$242.59	$242.60	$242.60
Purchase #6	$128.45	9.440%	$140.5757	$140.58	$140.60	$140.60
Purchase #7	$155.51	10.482%	$171.8106	$171.81	$171.80	$171.80
7 purchase totals =	$916.34		$998.3152	$998.33	$998.35	$998.30