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	$78.57	7.659%	$84.5877	$84.59	$84.60	$84.60
Purchase #2	$180.73	3.871%	$187.7261	$187.73	$187.75	$187.70
Purchase #3	$183.72	7.786%	$198.0244	$198.02	$198.00	$198.00
Purchase #4	$35.89	13.635%	$40.7836	$40.78	$40.80	$40.80
Purchase #5	$226.73	12.866%	$255.9011	$255.90	$255.90	$255.90
Purchase #6	$168.95	12.767%	$190.5198	$190.52	$190.50	$190.50
Purchase #7	$70.70	9.498%	$77.4151	$77.42	$77.40	$77.40
7 purchase totals =	$945.29		$1,034.9578	$1,034.96	$1,034.95	$1,034.90