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	$74.43	10.779%	$82.4528	$82.45	$82.45	$82.50
Purchase #2	$216.55	13.458%	$245.6933	$245.69	$245.70	$245.70
Purchase #3	$161.49	11.429%	$179.9467	$179.95	$179.95	$179.90
Purchase #4	$121.57	7.658%	$130.8798	$130.88	$130.90	$130.90
Purchase #5	$80.87	9.615%	$88.6457	$88.65	$88.65	$88.60
Purchase #6	$36.67	11.609%	$40.927	$40.93	$40.95	$40.90
Purchase #7	$11.38	5.146%	$11.9656	$11.97	$11.95	$12.00
7 purchase totals =	$702.96		$780.5109	$780.52	$780.55	$780.50