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	$152.43	11.508%	$169.9716	$169.97	$169.95	$170.00
Purchase #2	$172.90	12.141%	$193.8918	$193.89	$193.90	$193.90
Purchase #3	$75.37	4.172%	$78.5144	$78.51	$78.50	$78.50
Purchase #4	$18.75	13.664%	$21.312	$21.31	$21.30	$21.30
Purchase #5	$29.90	10.656%	$33.0861	$33.09	$33.10	$33.10
Purchase #6	$111.60	5.656%	$117.9121	$117.91	$117.90	$117.90
Purchase #7	$195.76	5.192%	$205.9239	$205.92	$205.90	$205.90
7 purchase totals =	$756.71		$820.6119	$820.60	$820.55	$820.60