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	$7.39	11.554%	$8.2438	$8.24	$8.25	$8.20
Purchase #2	$63.55	3.857%	$66.0011	$66.00	$66.00	$66.00
Purchase #3	$158.66	8.601%	$172.3063	$172.31	$172.30	$172.30
Purchase #4	$232.63	9.152%	$253.9203	$253.92	$253.90	$253.90
Purchase #5	$59.43	10.277%	$65.5376	$65.54	$65.55	$65.50
Purchase #6	$115.46	13.287%	$130.8012	$130.80	$130.80	$130.80
Purchase #7	$57.90	3.153%	$59.7256	$59.73	$59.75	$59.70
7 purchase totals =	$695.02		$756.5359	$756.54	$756.55	$756.40