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	$9.47	8.439%	$10.2692	$10.27	$10.25	$10.30
Purchase #2	$114.72	10.411%	$126.6635	$126.66	$126.65	$126.70
Purchase #3	$135.73	8.212%	$146.8761	$146.88	$146.90	$146.90
Purchase #4	$226.44	5.347%	$238.5477	$238.55	$238.55	$238.50
Purchase #5	$189.76	3.262%	$195.95	$195.95	$195.95	$196.00
Purchase #6	$46.52	4.118%	$48.4357	$48.44	$48.45	$48.40
Purchase #7	$65.46	3.152%	$67.5233	$67.52	$67.50	$67.50
7 purchase totals =	$788.10		$834.2655	$834.27	$834.25	$834.30