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 $137.47   10.193%   $151.4823   $151.48   $151.50   $151.50  
  Purchase #2 $151.26   8.324%   $163.8509   $163.85   $163.85   $163.90  
  Purchase #3 $113.81   7.564%   $122.4186   $122.42   $122.40   $122.40  
  Purchase #4 $156.61   8.504%   $169.9281   $169.93   $169.95   $169.90  
  Purchase #5 $63.99   12.116%   $71.743   $71.74   $71.75   $71.70  
  Purchase #6 $116.40   10.758%   $128.9223   $128.92   $128.90   $128.90  
  Purchase #7 $132.52   6.837%   $141.5804   $141.58   $141.60   $141.60  
  7 purchase totals = $872.06       $949.9256   $949.92   $949.95   $949.90