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	$144.96	9.606%	$158.8849	$158.88	$158.90	$158.90
Purchase #2	$218.77	11.706%	$244.3792	$244.38	$244.40	$244.40
Purchase #3	$103.64	7.542%	$111.4565	$111.46	$111.45	$111.50
Purchase #4	$206.37	3.602%	$213.8034	$213.80	$213.80	$213.80
Purchase #5	$243.38	5.107%	$255.8094	$255.81	$255.80	$255.80
Purchase #6	$70.81	5.244%	$74.5233	$74.52	$74.50	$74.50
Purchase #7	$216.67	4.756%	$226.9748	$226.97	$226.95	$227.00
7 purchase totals =	$1,204.60		$1,285.8315	$1,285.82	$1,285.80	$1,285.90