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	$139.32	12.429%	$156.6361	$156.64	$156.65	$156.60
Purchase #2	$193.75	12.769%	$218.4899	$218.49	$218.50	$218.50
Purchase #3	$145.47	6.811%	$155.378	$155.38	$155.40	$155.40
Purchase #4	$197.71	10.724%	$218.9124	$218.91	$218.90	$218.90
Purchase #5	$36.85	11.309%	$41.0174	$41.02	$41.00	$41.00
Purchase #6	$48.98	6.131%	$51.983	$51.98	$52.00	$52.00
Purchase #7	$196.39	10.520%	$217.0502	$217.05	$217.05	$217.10
7 purchase totals =	$958.47		$1,059.4670	$1,059.47	$1,059.50	$1,059.50