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	$17.55	5.183%	$18.4596	$18.46	$18.45	$18.50
Purchase #2	$151.88	10.618%	$168.0066	$168.01	$168.00	$168.00
Purchase #3	$68.57	6.198%	$72.82	$72.82	$72.80	$72.80
Purchase #4	$177.94	4.196%	$185.4064	$185.41	$185.40	$185.40
Purchase #5	$201.71	10.358%	$222.6031	$222.60	$222.60	$222.60
Purchase #6	$71.82	12.531%	$80.8198	$80.82	$80.80	$80.80
Purchase #7	$239.90	4.709%	$251.1969	$251.20	$251.20	$251.20
7 purchase totals =	$929.37		$999.3124	$999.32	$999.25	$999.30