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	$225.46	6.799%	$240.789	$240.79	$240.80	$240.80
Purchase #2	$193.80	13.307%	$219.589	$219.59	$219.60	$219.60
Purchase #3	$34.40	13.411%	$39.0134	$39.01	$39.00	$39.00
Purchase #4	$47.56	9.869%	$52.2537	$52.25	$52.25	$52.30
Purchase #5	$249.56	4.471%	$260.7178	$260.72	$260.70	$260.70
Purchase #6	$76.33	9.457%	$83.5485	$83.55	$83.55	$83.50
Purchase #7	$106.77	5.330%	$112.4608	$112.46	$112.45	$112.50
7 purchase totals =	$933.88		$1,008.3722	$1,008.37	$1,008.35	$1,008.40