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	$124.98	9.536%	$136.8981	$136.90	$136.90	$136.90
Purchase #2	$236.75	10.463%	$261.5212	$261.52	$261.50	$261.50
Purchase #3	$107.97	3.663%	$111.9249	$111.92	$111.90	$111.90
Purchase #4	$226.69	9.848%	$249.0144	$249.01	$249.00	$249.00
Purchase #5	$105.73	8.315%	$114.5214	$114.52	$114.50	$114.50
Purchase #6	$12.79	13.697%	$14.5418	$14.54	$14.55	$14.50
Purchase #7	$103.87	11.795%	$116.1215	$116.12	$116.10	$116.10
7 purchase totals =	$918.78		$1,004.5433	$1,004.53	$1,004.45	$1,004.40