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	$15.57	5.679%	$16.4542	$16.45	$16.45	$16.50
Purchase #2	$90.48	9.185%	$98.7906	$98.79	$98.80	$98.80
Purchase #3	$162.33	3.737%	$168.3963	$168.40	$168.40	$168.40
Purchase #4	$89.48	6.225%	$95.0501	$95.05	$95.05	$95.10
Purchase #5	$62.89	3.187%	$64.8943	$64.89	$64.90	$64.90
Purchase #6	$141.87	7.564%	$152.601	$152.60	$152.60	$152.60
Purchase #7	$99.38	12.589%	$111.8909	$111.89	$111.90	$111.90
7 purchase totals =	$662.00		$708.0774	$708.07	$708.10	$708.20