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	$125.30	6.709%	$133.7064	$133.71	$133.70	$133.70
Purchase #2	$69.67	3.382%	$72.0262	$72.03	$72.05	$72.00
Purchase #3	$148.65	10.590%	$164.392	$164.39	$164.40	$164.40
Purchase #4	$53.44	6.345%	$56.8308	$56.83	$56.85	$56.80
Purchase #5	$145.66	3.589%	$150.8877	$150.89	$150.90	$150.90
Purchase #6	$238.30	9.704%	$261.4246	$261.42	$261.40	$261.40
Purchase #7	$123.35	13.102%	$139.5113	$139.51	$139.50	$139.50
7 purchase totals =	$904.37		$978.7790	$978.78	$978.80	$978.70