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	$12.47	8.437%	$13.5221	$13.52	$13.50	$13.50
Purchase #2	$207.55	8.201%	$224.5712	$224.57	$224.55	$224.60
Purchase #3	$115.46	5.211%	$121.4766	$121.48	$121.50	$121.50
Purchase #4	$67.28	7.577%	$72.3778	$72.38	$72.40	$72.40
Purchase #5	$230.38	3.553%	$238.5654	$238.57	$238.55	$238.60
Purchase #6	$81.75	4.420%	$85.3634	$85.36	$85.35	$85.40
Purchase #7	$118.49	7.791%	$127.7216	$127.72	$127.70	$127.70
7 purchase totals =	$833.38		$883.5981	$883.60	$883.55	$883.70