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	$45.70	11.725%	$51.0583	$51.06	$51.05	$51.10
Purchase #2	$209.82	8.291%	$227.2162	$227.22	$227.20	$227.20
Purchase #3	$142.99	5.367%	$150.6643	$150.66	$150.65	$150.70
Purchase #4	$73.39	12.538%	$82.5916	$82.59	$82.60	$82.60
Purchase #5	$250.75	11.192%	$278.8139	$278.81	$278.80	$278.80
Purchase #6	$65.81	10.646%	$72.8161	$72.82	$72.80	$72.80
Purchase #7	$130.39	4.395%	$136.1206	$136.12	$136.10	$136.10
7 purchase totals =	$918.85		$999.2810	$999.28	$999.20	$999.30