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	$29.87	4.249%	$31.1392	$31.14	$31.15	$31.10
Purchase #2	$105.25	13.843%	$119.8198	$119.82	$119.80	$119.80
Purchase #3	$93.67	4.437%	$97.8261	$97.83	$97.85	$97.80
Purchase #4	$137.86	9.406%	$150.8271	$150.83	$150.85	$150.80
Purchase #5	$214.45	12.400%	$241.0418	$241.04	$241.05	$241.00
Purchase #6	$112.85	5.710%	$119.2937	$119.29	$119.30	$119.30
Purchase #7	$188.50	13.815%	$214.5413	$214.54	$214.55	$214.50
7 purchase totals =	$882.45		$974.4890	$974.49	$974.55	$974.30