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	$38.66	4.663%	$40.4627	$40.46	$40.45	$40.50
Purchase #2	$214.69	8.792%	$233.5655	$233.57	$233.55	$233.60
Purchase #3	$210.47	6.233%	$223.5886	$223.59	$223.60	$223.60
Purchase #4	$210.82	5.571%	$222.5648	$222.56	$222.55	$222.60
Purchase #5	$100.52	4.559%	$105.1027	$105.10	$105.10	$105.10
Purchase #6	$219.89	13.671%	$249.9512	$249.95	$249.95	$250.00
Purchase #7	$22.94	11.454%	$25.5675	$25.57	$25.55	$25.60
7 purchase totals =	$1,017.99		$1,100.8030	$1,100.80	$1,100.75	$1,101.00