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	$64.59	4.637%	$67.585	$67.59	$67.60	$67.60
Purchase #2	$240.58	5.540%	$253.9081	$253.91	$253.90	$253.90
Purchase #3	$105.83	9.641%	$116.0331	$116.03	$116.05	$116.00
Purchase #4	$250.37	12.157%	$280.8075	$280.81	$280.80	$280.80
Purchase #5	$12.47	7.846%	$13.4484	$13.45	$13.45	$13.40
Purchase #6	$206.87	11.364%	$230.3787	$230.38	$230.40	$230.40
Purchase #7	$19.73	5.273%	$20.7704	$20.77	$20.75	$20.80
7 purchase totals =	$900.44		$982.9312	$982.94	$982.95	$982.90