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	$51.77	5.636%	$54.6878	$54.69	$54.70	$54.70
Purchase #2	$242.71	7.185%	$260.1487	$260.15	$260.15	$260.10
Purchase #3	$107.45	4.126%	$111.8834	$111.88	$111.90	$111.90
Purchase #4	$175.91	3.670%	$182.3659	$182.37	$182.35	$182.40
Purchase #5	$249.78	12.441%	$280.8551	$280.86	$280.85	$280.90
Purchase #6	$118.35	7.390%	$127.0961	$127.10	$127.10	$127.10
Purchase #7	$233.27	13.800%	$265.4613	$265.46	$265.45	$265.50
7 purchase totals =	$1,179.24		$1,282.4983	$1,282.51	$1,282.50	$1,282.60