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 $51.62   12.422%   $58.0322   $58.03   $58.05   $58.00  
  Purchase #2 $107.83   11.194%   $119.9005   $119.90   $119.90   $119.90  
  Purchase #3 $125.77   5.504%   $132.6924   $132.69   $132.70   $132.70  
  Purchase #4 $193.42   4.727%   $202.563   $202.56   $202.55   $202.60  
  Purchase #5 $123.60   12.422%   $138.9536   $138.95   $138.95   $139.00  
  Purchase #6 $222.34   5.641%   $234.8822   $234.88   $234.90   $234.90  
  Purchase #7 $162.30   11.382%   $180.773   $180.77   $180.75   $180.80  
  7 purchase totals = $986.88       $1,067.7969   $1,067.78   $1,067.80   $1,067.90