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	$31.79	6.376%	$33.8169	$33.82	$33.80	$33.80
Purchase #2	$119.65	10.419%	$132.1163	$132.12	$132.10	$132.10
Purchase #3	$118.79	9.128%	$129.6332	$129.63	$129.65	$129.60
Purchase #4	$80.50	11.209%	$89.5232	$89.52	$89.50	$89.50
Purchase #5	$182.74	6.422%	$194.4756	$194.48	$194.50	$194.50
Purchase #6	$51.54	8.800%	$56.0755	$56.08	$56.10	$56.10
Purchase #7	$211.54	6.492%	$225.2732	$225.27	$225.25	$225.30
7 purchase totals =	$796.55		$860.9139	$860.92	$860.90	$860.90