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	$47.88	8.770%	$52.0791	$52.08	$52.10	$52.10
Purchase #2	$146.83	11.720%	$164.0385	$164.04	$164.05	$164.00
Purchase #3	$179.53	11.646%	$200.4381	$200.44	$200.45	$200.40
Purchase #4	$90.95	10.629%	$100.6171	$100.62	$100.60	$100.60
Purchase #5	$89.76	12.120%	$100.6389	$100.64	$100.65	$100.60
Purchase #6	$194.75	10.316%	$214.8404	$214.84	$214.85	$214.80
Purchase #7	$21.57	6.204%	$22.9082	$22.91	$22.90	$22.90
7 purchase totals =	$771.27		$855.5603	$855.57	$855.60	$855.40