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	$9.59	9.287%	$10.4806	$10.48	$10.50	$10.50
Purchase #2	$227.57	12.732%	$256.5442	$256.54	$256.55	$256.50
Purchase #3	$184.61	13.213%	$209.0025	$209.00	$209.00	$209.00
Purchase #4	$140.37	9.500%	$153.7052	$153.71	$153.70	$153.70
Purchase #5	$133.83	5.797%	$141.5881	$141.59	$141.60	$141.60
Purchase #6	$39.39	6.482%	$41.9433	$41.94	$41.95	$41.90
Purchase #7	$193.38	6.116%	$205.2071	$205.21	$205.20	$205.20
7 purchase totals =	$928.74		$1,018.4710	$1,018.47	$1,018.50	$1,018.40