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	$67.27	7.702%	$72.4511	$72.45	$72.45	$72.50
Purchase #2	$126.91	13.658%	$144.2434	$144.24	$144.25	$144.20
Purchase #3	$97.96	10.854%	$108.5926	$108.59	$108.60	$108.60
Purchase #4	$138.48	8.686%	$150.5084	$150.51	$150.50	$150.50
Purchase #5	$151.94	12.403%	$170.7851	$170.79	$170.80	$170.80
Purchase #6	$83.45	8.573%	$90.6042	$90.60	$90.60	$90.60
Purchase #7	$118.52	12.109%	$132.8716	$132.87	$132.85	$132.90
7 purchase totals =	$784.53		$870.0564	$870.05	$870.05	$870.10