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	$231.36	11.552%	$258.0867	$258.09	$258.10	$258.10
Purchase #2	$38.55	4.788%	$40.3958	$40.40	$40.40	$40.40
Purchase #3	$172.76	3.226%	$178.3332	$178.33	$178.35	$178.30
Purchase #4	$206.31	12.373%	$231.8367	$231.84	$231.85	$231.80
Purchase #5	$121.65	5.529%	$128.376	$128.38	$128.40	$128.40
Purchase #6	$136.27	3.668%	$141.2684	$141.27	$141.25	$141.30
Purchase #7	$72.89	11.794%	$81.4866	$81.49	$81.50	$81.50
7 purchase totals =	$979.79		$1,059.7834	$1,059.80	$1,059.85	$1,059.80