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	$72.51	11.571%	$80.9001	$80.90	$80.90	$80.90
Purchase #2	$69.72	5.377%	$73.4688	$73.47	$73.45	$73.50
Purchase #3	$130.82	10.481%	$144.5312	$144.53	$144.55	$144.50
Purchase #4	$14.74	7.189%	$15.7997	$15.80	$15.80	$15.80
Purchase #5	$46.83	10.786%	$51.8811	$51.88	$51.90	$51.90
Purchase #6	$52.69	6.639%	$56.1881	$56.19	$56.20	$56.20
Purchase #7	$71.62	10.260%	$78.9682	$78.97	$78.95	$79.00
7 purchase totals =	$458.93		$501.7372	$501.74	$501.75	$501.80