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	$122.89	13.789%	$139.8353	$139.84	$139.85	$139.80
Purchase #2	$103.33	3.791%	$107.2472	$107.25	$107.25	$107.20
Purchase #3	$179.31	11.477%	$199.8894	$199.89	$199.90	$199.90
Purchase #4	$203.69	13.581%	$231.3531	$231.35	$231.35	$231.40
Purchase #5	$48.86	5.284%	$51.4418	$51.44	$51.45	$51.40
Purchase #6	$19.76	3.799%	$20.5107	$20.51	$20.50	$20.50
Purchase #7	$244.26	5.392%	$257.4305	$257.43	$257.45	$257.40
7 purchase totals =	$922.10		$1,007.7080	$1,007.71	$1,007.75	$1,007.60