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	$221.92	10.775%	$245.8319	$245.83	$245.85	$245.80
Purchase #2	$144.50	5.689%	$152.7206	$152.72	$152.70	$152.70
Purchase #3	$102.71	5.509%	$108.3683	$108.37	$108.35	$108.40
Purchase #4	$104.95	6.179%	$111.4349	$111.43	$111.45	$111.40
Purchase #5	$156.40	7.331%	$167.8657	$167.87	$167.85	$167.90
Purchase #6	$142.62	12.524%	$160.4817	$160.48	$160.50	$160.50
Purchase #7	$11.38	3.556%	$11.7847	$11.78	$11.80	$11.80
7 purchase totals =	$884.48		$958.4878	$958.48	$958.50	$958.50