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 $105.61   8.442%   $114.5256   $114.53   $114.55   $114.50  
  Purchase #2 $136.99   11.196%   $152.3274   $152.33   $152.35   $152.30  
  Purchase #3 $114.54   6.143%   $121.5762   $121.58   $121.60   $121.60  
  Purchase #4 $229.71   5.459%   $242.2499   $242.25   $242.25   $242.20  
  Purchase #5 $170.89   13.644%   $194.2062   $194.21   $194.20   $194.20  
  Purchase #6 $114.26   6.832%   $122.0662   $122.07   $122.05   $122.10  
  Purchase #7 $25.63   12.685%   $28.8812   $28.88   $28.90   $28.90  
  7 purchase totals = $897.63       $975.8327   $975.85   $975.90   $975.80