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	$36.45	8.801%	$39.658	$39.66	$39.65	$39.70
Purchase #2	$214.37	13.273%	$242.8233	$242.82	$242.80	$242.80
Purchase #3	$5.93	10.597%	$6.5584	$6.56	$6.55	$6.60
Purchase #4	$59.93	12.767%	$67.5813	$67.58	$67.60	$67.60
Purchase #5	$133.48	8.253%	$144.4961	$144.50	$144.50	$144.50
Purchase #6	$63.25	6.678%	$67.4738	$67.47	$67.45	$67.50
Purchase #7	$178.95	10.604%	$197.9259	$197.93	$197.95	$197.90
7 purchase totals =	$692.36		$766.5168	$766.52	$766.50	$766.60