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	$177.59	3.618%	$184.0152	$184.02	$184.00	$184.00
Purchase #2	$55.55	4.125%	$57.8414	$57.84	$57.85	$57.80
Purchase #3	$199.94	12.643%	$225.2184	$225.22	$225.20	$225.20
Purchase #4	$140.70	11.536%	$156.9312	$156.93	$156.95	$156.90
Purchase #5	$35.88	7.611%	$38.6108	$38.61	$38.60	$38.60
Purchase #6	$19.50	10.208%	$21.4906	$21.49	$21.50	$21.50
Purchase #7	$142.39	5.840%	$150.7056	$150.71	$150.70	$150.70
7 purchase totals =	$771.55		$834.8132	$834.82	$834.80	$834.70