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	$31.27	9.237%	$34.1584	$34.16	$34.15	$34.20
Purchase #2	$138.90	4.365%	$144.963	$144.96	$144.95	$145.00
Purchase #3	$80.46	10.624%	$89.0081	$89.01	$89.00	$89.00
Purchase #4	$56.50	7.677%	$60.8375	$60.84	$60.85	$60.80
Purchase #5	$92.98	7.762%	$100.1971	$100.20	$100.20	$100.20
Purchase #6	$54.75	4.359%	$57.1366	$57.14	$57.15	$57.10
Purchase #7	$105.91	11.562%	$118.1553	$118.16	$118.15	$118.20
7 purchase totals =	$560.77		$604.4560	$604.47	$604.45	$604.50