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 $242.89   7.588%   $261.3205   $261.32   $261.30   $261.30  
  Purchase #2 $114.79   10.378%   $126.7029   $126.70   $126.70   $126.70  
  Purchase #3 $16.84   10.720%   $18.6452   $18.65   $18.65   $18.60  
  Purchase #4 $24.61   10.323%   $27.1505   $27.15   $27.15   $27.20  
  Purchase #5 $97.58   12.609%   $109.8839   $109.88   $109.90   $109.90  
  Purchase #6 $225.96   13.146%   $255.6647   $255.66   $255.65   $255.70  
  Purchase #7 $208.40   13.642%   $236.8299   $236.83   $236.85   $236.80  
  7 purchase totals = $931.07       $1,036.1976   $1,036.19   $1,036.20   $1,036.20