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	$38.40	13.271%	$43.4961	$43.50	$43.50	$43.50
Purchase #2	$14.78	7.320%	$15.8619	$15.86	$15.85	$15.90
Purchase #3	$164.74	10.146%	$181.4545	$181.45	$181.45	$181.50
Purchase #4	$242.74	11.684%	$271.1017	$271.10	$271.10	$271.10
Purchase #5	$208.29	9.475%	$228.0255	$228.03	$228.05	$228.00
Purchase #6	$184.63	8.357%	$200.0595	$200.06	$200.05	$200.10
Purchase #7	$192.94	9.284%	$210.8525	$210.85	$210.85	$210.90
7 purchase totals =	$1,046.52		$1,150.8517	$1,150.85	$1,150.85	$1,151.00