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 $42.30   11.846%   $47.3109   $47.31   $47.30   $47.30  
  Purchase #2 $239.62   9.532%   $262.4606   $262.46   $262.45   $262.50  
  Purchase #3 $72.99   12.639%   $82.2152   $82.22   $82.20   $82.20  
  Purchase #4 $209.88   12.588%   $236.2997   $236.30   $236.30   $236.30  
  Purchase #5 $24.48   4.610%   $25.6085   $25.61   $25.60   $25.60  
  Purchase #6 $28.76   4.323%   $30.0033   $30.00   $30.00   $30.00  
  Purchase #7 $247.80   13.268%   $280.6781   $280.68   $280.70   $280.70  
  7 purchase totals = $865.83       $964.5763   $964.58   $964.55   $964.60