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 $66.63   10.624%   $73.7088   $73.71   $73.70   $73.70  
  Purchase #2 $100.89   7.212%   $108.1662   $108.17   $108.15   $108.20  
  Purchase #3 $180.53   5.768%   $190.943   $190.94   $190.95   $190.90  
  Purchase #4 $42.28   9.716%   $46.3879   $46.39   $46.40   $46.40  
  Purchase #5 $209.51   8.608%   $227.5446   $227.54   $227.55   $227.50  
  Purchase #6 $195.31   12.270%   $219.2745   $219.27   $219.25   $219.30  
  Purchase #7 $66.47   4.244%   $69.291   $69.29   $69.30   $69.30  
  7 purchase totals = $861.62       $935.3160   $935.31   $935.30   $935.30