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	$116.99	12.303%	$131.3833	$131.38	$131.40	$131.40
Purchase #2	$234.91	12.625%	$264.5674	$264.57	$264.55	$264.60
Purchase #3	$53.83	8.868%	$58.6036	$58.60	$58.60	$58.60
Purchase #4	$108.70	4.768%	$113.8828	$113.88	$113.90	$113.90
Purchase #5	$82.48	7.252%	$88.4614	$88.46	$88.45	$88.50
Purchase #6	$11.94	5.859%	$12.6396	$12.64	$12.65	$12.60
Purchase #7	$169.85	12.193%	$190.5598	$190.56	$190.55	$190.60
7 purchase totals =	$778.70		$860.0979	$860.09	$860.10	$860.20