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 $87.61   10.236%   $96.5778   $96.58   $96.60   $96.60  
  Purchase #2 $125.96   10.377%   $139.0309   $139.03   $139.05   $139.00  
  Purchase #3 $208.45   3.170%   $215.0579   $215.06   $215.05   $215.10  
  Purchase #4 $71.62   9.868%   $78.6875   $78.69   $78.70   $78.70  
  Purchase #5 $66.94   10.355%   $73.8716   $73.87   $73.85   $73.90  
  Purchase #6 $56.63   9.432%   $61.9713   $61.97   $61.95   $62.00  
  Purchase #7 $178.71   12.511%   $201.0684   $201.07   $201.05   $201.10  
  7 purchase totals = $795.92       $866.2654   $866.27   $866.25   $866.40