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	$55.93	5.517%	$59.0157	$59.02	$59.00	$59.00
Purchase #2	$250.55	13.605%	$284.6373	$284.64	$284.65	$284.60
Purchase #3	$123.86	10.601%	$136.9904	$136.99	$137.00	$137.00
Purchase #4	$175.30	3.325%	$181.1287	$181.13	$181.15	$181.10
Purchase #5	$70.90	10.383%	$78.2615	$78.26	$78.25	$78.30
Purchase #6	$126.76	13.351%	$143.6837	$143.68	$143.70	$143.70
Purchase #7	$108.31	13.388%	$122.8105	$122.81	$122.80	$122.80
7 purchase totals =	$911.61		$1,006.5278	$1,006.53	$1,006.55	$1,006.50