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	$146.43	6.847%	$156.4561	$156.46	$156.45	$156.50
Purchase #2	$21.59	13.397%	$24.4824	$24.48	$24.50	$24.50
Purchase #3	$33.62	11.470%	$37.4762	$37.48	$37.50	$37.50
Purchase #4	$190.70	12.529%	$214.5928	$214.59	$214.60	$214.60
Purchase #5	$19.61	10.757%	$21.7194	$21.72	$21.70	$21.70
Purchase #6	$89.99	7.823%	$97.0299	$97.03	$97.05	$97.00
Purchase #7	$11.64	7.372%	$12.4981	$12.50	$12.50	$12.50
7 purchase totals =	$513.58		$564.2549	$564.26	$564.30	$564.30