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	$38.31	10.749%	$42.4279	$42.43	$42.45	$42.40
Purchase #2	$79.67	9.828%	$87.5	$87.50	$87.50	$87.50
Purchase #3	$81.76	10.857%	$90.6367	$90.64	$90.65	$90.60
Purchase #4	$200.83	13.179%	$227.2974	$227.30	$227.30	$227.30
Purchase #5	$21.50	9.339%	$23.5079	$23.51	$23.50	$23.50
Purchase #6	$139.26	8.531%	$151.1403	$151.14	$151.15	$151.10
Purchase #7	$61.69	3.642%	$63.9367	$63.94	$63.95	$63.90
7 purchase totals =	$623.02		$686.4469	$686.46	$686.50	$686.30