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	$16.79	4.118%	$17.4814	$17.48	$17.50	$17.50
Purchase #2	$234.79	3.577%	$243.1884	$243.19	$243.20	$243.20
Purchase #3	$239.66	6.417%	$255.039	$255.04	$255.05	$255.00
Purchase #4	$178.86	9.605%	$196.0395	$196.04	$196.05	$196.00
Purchase #5	$176.46	11.105%	$196.0559	$196.06	$196.05	$196.10
Purchase #6	$19.73	8.153%	$21.3386	$21.34	$21.35	$21.30
Purchase #7	$46.37	6.845%	$49.544	$49.54	$49.55	$49.50
7 purchase totals =	$912.66		$978.6868	$978.69	$978.75	$978.60