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 $241.72   7.486%   $259.8152   $259.82   $259.80   $259.80  
  Purchase #2 $195.86   6.467%   $208.5263   $208.53   $208.55   $208.50  
  Purchase #3 $244.32   6.866%   $261.095   $261.10   $261.10   $261.10  
  Purchase #4 $179.30   13.301%   $203.1487   $203.15   $203.15   $203.10  
  Purchase #5 $211.50   3.400%   $218.691   $218.69   $218.70   $218.70  
  Purchase #6 $44.39   5.444%   $46.8066   $46.81   $46.80   $46.80  
  Purchase #7 $20.57   9.675%   $22.5601   $22.56   $22.55   $22.60  
  7 purchase totals = $1,137.66       $1,220.6429   $1,220.66   $1,220.65   $1,220.60