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	$37.45	12.723%	$42.2148	$42.21	$42.20	$42.20
Purchase #2	$10.55	6.525%	$11.2384	$11.24	$11.25	$11.20
Purchase #3	$29.79	12.580%	$33.5376	$33.54	$33.55	$33.50
Purchase #4	$77.69	4.870%	$81.4735	$81.47	$81.45	$81.50
Purchase #5	$217.48	13.502%	$246.8441	$246.84	$246.85	$246.80
Purchase #6	$189.51	5.439%	$199.8174	$199.82	$199.80	$199.80
Purchase #7	$45.77	10.678%	$50.6573	$50.66	$50.65	$50.70
7 purchase totals =	$608.24		$665.7831	$665.78	$665.75	$665.70