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 $39.71   5.716%   $41.9798   $41.98   $42.00   $42.00  
  Purchase #2 $242.49   13.519%   $275.2722   $275.27   $275.25   $275.30  
  Purchase #3 $10.73   13.377%   $12.1654   $12.17   $12.15   $12.20  
  Purchase #4 $61.90   5.614%   $65.3751   $65.38   $65.40   $65.40  
  Purchase #5 $15.77   11.293%   $17.5509   $17.55   $17.55   $17.60  
  Purchase #6 $246.79   13.457%   $280.0005   $280.00   $280.00   $280.00  
  Purchase #7 $208.72   11.439%   $232.5955   $232.60   $232.60   $232.60  
  7 purchase totals = $826.11       $924.9394   $924.95   $924.95   $925.10