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	$235.33	8.759%	$255.9426	$255.94	$255.95	$255.90
Purchase #2	$242.40	4.559%	$253.451	$253.45	$253.45	$253.50
Purchase #3	$139.30	5.438%	$146.8751	$146.88	$146.90	$146.90
Purchase #4	$59.89	13.263%	$67.8332	$67.83	$67.85	$67.80
Purchase #5	$234.96	11.521%	$262.0297	$262.03	$262.05	$262.00
Purchase #6	$139.33	12.183%	$156.3046	$156.30	$156.30	$156.30
Purchase #7	$214.60	4.739%	$224.7699	$224.77	$224.75	$224.80
7 purchase totals =	$1,265.81		$1,367.2061	$1,367.20	$1,367.25	$1,367.20