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	$125.40	11.537%	$139.8674	$139.87	$139.85	$139.90
Purchase #2	$228.69	11.759%	$255.5817	$255.58	$255.60	$255.60
Purchase #3	$204.71	9.863%	$224.9005	$224.90	$224.90	$224.90
Purchase #4	$105.45	10.582%	$116.6087	$116.61	$116.60	$116.60
Purchase #5	$179.63	11.646%	$200.5497	$200.55	$200.55	$200.50
Purchase #6	$34.62	3.445%	$35.8127	$35.81	$35.80	$35.80
Purchase #7	$67.64	3.550%	$70.0412	$70.04	$70.05	$70.00
7 purchase totals =	$946.14		$1,043.3619	$1,043.36	$1,043.35	$1,043.30