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	$230.27	12.265%	$258.5126	$258.51	$258.50	$258.50
Purchase #2	$69.80	5.872%	$73.8987	$73.90	$73.90	$73.90
Purchase #3	$143.57	8.337%	$155.5394	$155.54	$155.55	$155.50
Purchase #4	$114.50	4.828%	$120.0281	$120.03	$120.05	$120.00
Purchase #5	$20.77	3.718%	$21.5422	$21.54	$21.55	$21.50
Purchase #6	$189.89	3.489%	$196.5153	$196.52	$196.50	$196.50
Purchase #7	$68.73	8.624%	$74.6573	$74.66	$74.65	$74.70
7 purchase totals =	$837.53		$900.6936	$900.70	$900.70	$900.60