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	$107.36	10.276%	$118.3923	$118.39	$118.40	$118.40
Purchase #2	$140.76	5.641%	$148.7003	$148.70	$148.70	$148.70
Purchase #3	$63.94	13.870%	$72.8085	$72.81	$72.80	$72.80
Purchase #4	$105.66	5.737%	$111.7217	$111.72	$111.70	$111.70
Purchase #5	$164.80	12.499%	$185.3984	$185.40	$185.40	$185.40
Purchase #6	$119.45	8.390%	$129.4719	$129.47	$129.45	$129.50
Purchase #7	$107.72	13.782%	$122.566	$122.57	$122.55	$122.60
7 purchase totals =	$809.69		$889.0591	$889.06	$889.00	$889.10