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	$47.59	6.214%	$50.5472	$50.55	$50.55	$50.50
Purchase #2	$121.43	5.821%	$128.4984	$128.50	$128.50	$128.50
Purchase #3	$39.76	11.251%	$44.2334	$44.23	$44.25	$44.20
Purchase #4	$236.58	4.200%	$246.5164	$246.52	$246.50	$246.50
Purchase #5	$105.60	3.790%	$109.6022	$109.60	$109.60	$109.60
Purchase #6	$127.25	8.276%	$137.7812	$137.78	$137.80	$137.80
Purchase #7	$183.70	9.257%	$200.7051	$200.71	$200.70	$200.70
7 purchase totals =	$861.91		$917.8839	$917.89	$917.90	$917.80