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	$193.91	7.448%	$208.3524	$208.35	$208.35	$208.40
Purchase #2	$212.96	12.717%	$240.0421	$240.04	$240.05	$240.00
Purchase #3	$179.92	11.490%	$200.5928	$200.59	$200.60	$200.60
Purchase #4	$189.98	3.439%	$196.5134	$196.51	$196.50	$196.50
Purchase #5	$42.72	9.640%	$46.8382	$46.84	$46.85	$46.80
Purchase #6	$44.96	6.548%	$47.904	$47.90	$47.90	$47.90
Purchase #7	$48.84	4.139%	$50.8615	$50.86	$50.85	$50.90
7 purchase totals =	$913.29		$991.1044	$991.09	$991.10	$991.10