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 $56.84   7.571%   $61.1434   $61.14   $61.15   $61.10  
  Purchase #2 $227.86   6.606%   $242.9124   $242.91   $242.90   $242.90  
  Purchase #3 $75.41   6.797%   $80.5356   $80.54   $80.55   $80.50  
  Purchase #4 $201.46   3.560%   $208.632   $208.63   $208.65   $208.60  
  Purchase #5 $96.36   7.631%   $103.7132   $103.71   $103.70   $103.70  
  Purchase #6 $85.70   5.661%   $90.5515   $90.55   $90.55   $90.60  
  Purchase #7 $9.51   12.785%   $10.7259   $10.73   $10.75   $10.70  
  7 purchase totals = $753.14       $798.2140   $798.21   $798.25   $798.10