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 $247.50   5.584%   $261.3204   $261.32   $261.30   $261.30  
  Purchase #2 $236.81   13.290%   $268.282   $268.28   $268.30   $268.30  
  Purchase #3 $215.79   12.469%   $242.6969   $242.70   $242.70   $242.70  
  Purchase #4 $9.26   3.503%   $9.5844   $9.58   $9.60   $9.60  
  Purchase #5 $65.31   3.871%   $67.8382   $67.84   $67.85   $67.80  
  Purchase #6 $160.68   6.673%   $171.4022   $171.40   $171.40   $171.40  
  Purchase #7 $20.67   13.819%   $23.5264   $23.53   $23.55   $23.50  
  7 purchase totals = $956.02       $1,044.6505   $1,044.65   $1,044.70   $1,044.60