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 $23.69   3.819%   $24.5947   $24.59   $24.60   $24.60  
  Purchase #2 $250.56   6.730%   $267.4227   $267.42   $267.40   $267.40  
  Purchase #3 $119.65   5.819%   $126.6124   $126.61   $126.60   $126.60  
  Purchase #4 $85.73   8.601%   $93.1036   $93.10   $93.10   $93.10  
  Purchase #5 $241.64   3.226%   $249.4353   $249.44   $249.45   $249.40  
  Purchase #6 $144.54   13.464%   $164.0009   $164.00   $164.00   $164.00  
  Purchase #7 $224.59   5.323%   $236.5449   $236.54   $236.55   $236.50  
  7 purchase totals = $1,090.40       $1,161.7145   $1,161.70   $1,161.70   $1,161.60