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	$30.34	12.553%	$34.1486	$34.15	$34.15	$34.10
Purchase #2	$103.59	12.839%	$116.8899	$116.89	$116.90	$116.90
Purchase #3	$238.74	8.313%	$258.5865	$258.59	$258.60	$258.60
Purchase #4	$108.80	13.791%	$123.8046	$123.80	$123.80	$123.80
Purchase #5	$80.93	11.768%	$90.4538	$90.45	$90.45	$90.50
Purchase #6	$165.95	8.418%	$179.9197	$179.92	$179.90	$179.90
Purchase #7	$129.80	9.396%	$141.996	$142.00	$142.00	$142.00
7 purchase totals =	$858.15		$945.7991	$945.80	$945.80	$945.80