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	$172.96	9.323%	$189.0851	$189.09	$189.10	$189.10
Purchase #2	$28.66	10.763%	$31.7447	$31.74	$31.75	$31.70
Purchase #3	$70.42	10.289%	$77.6655	$77.67	$77.65	$77.70
Purchase #4	$192.25	13.822%	$218.8228	$218.82	$218.80	$218.80
Purchase #5	$155.96	12.826%	$175.9634	$175.96	$175.95	$176.00
Purchase #6	$214.71	11.266%	$238.8992	$238.90	$238.90	$238.90
Purchase #7	$40.29	13.747%	$45.8287	$45.83	$45.85	$45.80
7 purchase totals =	$875.25		$978.0094	$978.01	$978.00	$978.00