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	$45.89	10.785%	$50.8392	$50.84	$50.85	$50.80
Purchase #2	$94.81	8.676%	$103.0357	$103.04	$103.05	$103.00
Purchase #3	$76.85	9.126%	$83.8633	$83.86	$83.85	$83.90
Purchase #4	$212.76	7.546%	$228.8149	$228.81	$228.80	$228.80
Purchase #5	$213.76	7.403%	$229.5847	$229.58	$229.60	$229.60
Purchase #6	$184.86	8.550%	$200.6655	$200.67	$200.65	$200.70
Purchase #7	$147.33	7.645%	$158.5934	$158.59	$158.60	$158.60
7 purchase totals =	$976.26		$1,055.3967	$1,055.39	$1,055.40	$1,055.40