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 $82.83   12.777%   $93.4132   $93.41   $93.40   $93.40  
  Purchase #2 $114.52   8.461%   $124.2095   $124.21   $124.20   $124.20  
  Purchase #3 $13.88   6.161%   $14.7351   $14.74   $14.75   $14.70  
  Purchase #4 $82.69   9.638%   $90.6597   $90.66   $90.65   $90.70  
  Purchase #5 $151.42   4.158%   $157.716   $157.72   $157.70   $157.70  
  Purchase #6 $242.27   6.821%   $258.7952   $258.80   $258.80   $258.80  
  Purchase #7 $68.91   9.677%   $75.5784   $75.58   $75.60   $75.60  
  7 purchase totals = $756.52       $815.1071   $815.12   $815.10   $815.10