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	$111.72	9.236%	$122.0385	$122.04	$122.05	$122.00
Purchase #2	$199.31	8.333%	$215.9185	$215.92	$215.90	$215.90
Purchase #3	$81.83	9.496%	$89.6006	$89.60	$89.60	$89.60
Purchase #4	$81.65	10.107%	$89.9024	$89.90	$89.90	$89.90
Purchase #5	$62.78	6.700%	$66.9863	$66.99	$67.00	$67.00
Purchase #6	$228.79	13.645%	$260.0084	$260.01	$260.00	$260.00
Purchase #7	$40.72	13.171%	$46.0832	$46.08	$46.10	$46.10
7 purchase totals =	$806.80		$890.5379	$890.54	$890.55	$890.50