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 $58.85   3.527%   $60.9256   $60.93   $60.95   $60.90  
  Purchase #2 $15.44   6.473%   $16.4394   $16.44   $16.45   $16.40  
  Purchase #3 $231.90   9.418%   $253.7403   $253.74   $253.75   $253.70  
  Purchase #4 $93.29   12.648%   $105.0893   $105.09   $105.10   $105.10  
  Purchase #5 $67.84   5.676%   $71.6906   $71.69   $71.70   $71.70  
  Purchase #6 $57.72   4.739%   $60.4554   $60.46   $60.45   $60.50  
  Purchase #7 $215.56   9.553%   $236.1524   $236.15   $236.15   $236.20  
  7 purchase totals = $740.60       $804.4930   $804.50   $804.55   $804.50