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	$10.95	10.384%	$12.087	$12.09	$12.10	$12.10
Purchase #2	$139.80	11.828%	$156.3355	$156.34	$156.35	$156.30
Purchase #3	$140.84	13.273%	$159.5337	$159.53	$159.55	$159.50
Purchase #4	$132.50	13.816%	$150.8062	$150.81	$150.80	$150.80
Purchase #5	$64.95	11.226%	$72.2413	$72.24	$72.25	$72.20
Purchase #6	$120.54	8.743%	$131.0788	$131.08	$131.10	$131.10
Purchase #7	$30.86	9.602%	$33.8232	$33.82	$33.80	$33.80
7 purchase totals =	$640.44		$715.9057	$715.91	$715.95	$715.80