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 $207.53   9.843%   $227.9572   $227.96   $227.95   $228.00  
  Purchase #2 $36.86   6.506%   $39.2581   $39.26   $39.25   $39.30  
  Purchase #3 $21.92   9.696%   $24.0454   $24.05   $24.05   $24.00  
  Purchase #4 $17.89   6.512%   $19.055   $19.06   $19.05   $19.10  
  Purchase #5 $132.41   12.174%   $148.5296   $148.53   $148.55   $148.50  
  Purchase #6 $46.97   10.711%   $52.001   $52.00   $52.00   $52.00  
  Purchase #7 $133.59   10.854%   $148.0899   $148.09   $148.10   $148.10  
  7 purchase totals = $597.17       $658.9362   $658.95   $658.95   $659.00