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	$245.40	4.359%	$256.097	$256.10	$256.10	$256.10
Purchase #2	$18.77	8.546%	$20.3741	$20.37	$20.35	$20.40
Purchase #3	$10.61	9.798%	$11.6496	$11.65	$11.65	$11.60
Purchase #4	$67.29	3.517%	$69.6566	$69.66	$69.65	$69.70
Purchase #5	$181.68	4.859%	$190.5078	$190.51	$190.50	$190.50
Purchase #6	$45.32	3.496%	$46.9044	$46.90	$46.90	$46.90
Purchase #7	$105.59	6.730%	$112.6962	$112.70	$112.70	$112.70
7 purchase totals =	$674.66		$707.8857	$707.89	$707.85	$707.90