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	$250.47	10.569%	$276.9422	$276.94	$276.95	$276.90
Purchase #2	$56.46	5.469%	$59.5478	$59.55	$59.55	$59.50
Purchase #3	$199.99	6.449%	$212.8874	$212.89	$212.90	$212.90
Purchase #4	$31.78	8.338%	$34.4298	$34.43	$34.45	$34.40
Purchase #5	$136.97	5.119%	$143.9815	$143.98	$144.00	$144.00
Purchase #6	$64.35	6.723%	$68.6763	$68.68	$68.70	$68.70
Purchase #7	$93.44	7.859%	$100.7834	$100.78	$100.80	$100.80
7 purchase totals =	$833.46		$897.2484	$897.25	$897.35	$897.20