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 $231.26   11.590%   $258.063   $258.06   $258.05   $258.10  
  Purchase #2 $54.57   6.558%   $58.1487   $58.15   $58.15   $58.10  
  Purchase #3 $214.62   3.236%   $221.5651   $221.57   $221.55   $221.60  
  Purchase #4 $217.58   4.758%   $227.9325   $227.93   $227.95   $227.90  
  Purchase #5 $131.53   7.761%   $141.738   $141.74   $141.75   $141.70  
  Purchase #6 $234.31   6.703%   $250.0158   $250.02   $250.00   $250.00  
  Purchase #7 $222.65   11.186%   $247.5556   $247.56   $247.55   $247.60  
  7 purchase totals = $1,306.52       $1,405.0187   $1,405.03   $1,405.00   $1,405.00