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 $114.58   4.253%   $119.4531   $119.45   $119.45   $119.50  
  Purchase #2 $178.63   9.637%   $195.8446   $195.84   $195.85   $195.80  
  Purchase #3 $35.69   13.874%   $40.6416   $40.64   $40.65   $40.60  
  Purchase #4 $51.68   3.645%   $53.5637   $53.56   $53.55   $53.60  
  Purchase #5 $153.71   6.105%   $163.094   $163.09   $163.10   $163.10  
  Purchase #6 $136.91   13.564%   $155.4805   $155.48   $155.50   $155.50  
  Purchase #7 $235.39   5.184%   $247.5926   $247.59   $247.60   $247.60  
  7 purchase totals = $906.59       $975.6701   $975.65   $975.70   $975.70