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	$159.71	3.120%	$164.693	$164.69	$164.70	$164.70
Purchase #2	$80.61	12.230%	$90.4686	$90.47	$90.45	$90.50
Purchase #3	$78.39	3.565%	$81.1846	$81.18	$81.20	$81.20
Purchase #4	$35.78	8.492%	$38.8184	$38.82	$38.80	$38.80
Purchase #5	$101.76	6.720%	$108.5983	$108.60	$108.60	$108.60
Purchase #6	$223.79	9.629%	$245.3387	$245.34	$245.35	$245.30
Purchase #7	$124.60	6.340%	$132.4996	$132.50	$132.50	$132.50
7 purchase totals =	$804.64		$861.6012	$861.60	$861.60	$861.60