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	$95.98	11.186%	$106.7163	$106.72	$106.70	$106.70
Purchase #2	$147.47	11.768%	$164.8243	$164.82	$164.80	$164.80
Purchase #3	$19.39	12.295%	$21.774	$21.77	$21.75	$21.80
Purchase #4	$159.45	4.116%	$166.013	$166.01	$166.00	$166.00
Purchase #5	$245.82	12.184%	$275.7707	$275.77	$275.75	$275.80
Purchase #6	$82.91	9.693%	$90.9465	$90.95	$90.95	$90.90
Purchase #7	$150.52	9.386%	$164.6478	$164.65	$164.65	$164.60
7 purchase totals =	$901.54		$990.6926	$990.69	$990.60	$990.60