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	$152.43	3.769%	$158.1751	$158.18	$158.20	$158.20
Purchase #2	$248.49	8.869%	$270.5286	$270.53	$270.55	$270.50
Purchase #3	$107.96	7.848%	$116.4327	$116.43	$116.45	$116.40
Purchase #4	$237.55	13.698%	$270.0896	$270.09	$270.10	$270.10
Purchase #5	$178.64	7.206%	$191.5128	$191.51	$191.50	$191.50
Purchase #6	$19.94	4.622%	$20.8616	$20.86	$20.85	$20.90
Purchase #7	$167.76	11.177%	$186.5105	$186.51	$186.50	$186.50
7 purchase totals =	$1,112.77		$1,214.1109	$1,214.11	$1,214.15	$1,214.10