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	$99.59	3.286%	$102.8625	$102.86	$102.85	$102.90
Purchase #2	$204.60	5.208%	$215.2556	$215.26	$215.25	$215.30
Purchase #3	$222.83	10.128%	$245.3982	$245.40	$245.40	$245.40
Purchase #4	$150.65	4.544%	$157.4955	$157.50	$157.50	$157.50
Purchase #5	$104.89	4.706%	$109.8261	$109.83	$109.85	$109.80
Purchase #6	$138.83	7.166%	$148.7786	$148.78	$148.80	$148.80
Purchase #7	$110.64	5.184%	$116.3756	$116.38	$116.40	$116.40
7 purchase totals =	$1,032.03		$1,095.9921	$1,096.01	$1,096.05	$1,096.10