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	$128.93	6.786%	$137.6792	$137.68	$137.70	$137.70
Purchase #2	$61.86	8.633%	$67.2004	$67.20	$67.20	$67.20
Purchase #3	$183.96	4.720%	$192.6429	$192.64	$192.65	$192.60
Purchase #4	$171.61	13.482%	$194.7465	$194.75	$194.75	$194.70
Purchase #5	$85.70	4.516%	$89.5702	$89.57	$89.55	$89.60
Purchase #6	$40.99	6.161%	$43.5154	$43.52	$43.50	$43.50
Purchase #7	$59.61	5.806%	$63.071	$63.07	$63.05	$63.10
7 purchase totals =	$732.66		$788.4256	$788.43	$788.40	$788.40