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	$138.81	12.324%	$155.9169	$155.92	$155.90	$155.90
Purchase #2	$70.53	11.845%	$78.8843	$78.88	$78.90	$78.90
Purchase #3	$182.88	13.123%	$206.8793	$206.88	$206.90	$206.90
Purchase #4	$120.95	13.284%	$137.017	$137.02	$137.00	$137.00
Purchase #5	$75.86	9.754%	$83.2594	$83.26	$83.25	$83.30
Purchase #6	$134.97	7.202%	$144.6905	$144.69	$144.70	$144.70
Purchase #7	$133.71	7.520%	$143.765	$143.77	$143.75	$143.80
7 purchase totals =	$857.71		$950.4124	$950.42	$950.40	$950.50