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 $207.84   3.699%   $215.528   $215.53   $215.55   $215.50  
  Purchase #2 $54.75   11.500%   $61.0463   $61.05   $61.05   $61.00  
  Purchase #3 $32.85   13.786%   $37.3787   $37.38   $37.40   $37.40  
  Purchase #4 $26.26   8.692%   $28.5425   $28.54   $28.55   $28.50  
  Purchase #5 $244.73   11.598%   $273.1138   $273.11   $273.10   $273.10  
  Purchase #6 $154.65   4.516%   $161.634   $161.63   $161.65   $161.60  
  Purchase #7 $234.25   9.783%   $257.1667   $257.17   $257.15   $257.20  
  7 purchase totals = $955.33       $1,034.4100   $1,034.41   $1,034.45   $1,034.30