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 $53.62   8.455%   $58.1536   $58.15   $58.15   $58.20  
  Purchase #2 $122.41   11.619%   $136.6328   $136.63   $136.65   $136.60  
  Purchase #3 $68.79   11.433%   $76.6548   $76.65   $76.65   $76.70  
  Purchase #4 $234.48   9.649%   $257.105   $257.11   $257.10   $257.10  
  Purchase #5 $192.99   11.761%   $215.6876   $215.69   $215.70   $215.70  
  Purchase #6 $129.95   3.692%   $134.7478   $134.75   $134.75   $134.70  
  Purchase #7 $99.49   3.659%   $103.1303   $103.13   $103.15   $103.10  
  7 purchase totals = $901.73       $982.1119   $982.11   $982.15   $982.10