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 $238.86   6.240%   $253.7649   $253.76   $253.75   $253.80  
  Purchase #2 $218.48   4.299%   $227.8725   $227.87   $227.85   $227.90  
  Purchase #3 $174.25   3.159%   $179.7546   $179.75   $179.75   $179.80  
  Purchase #4 $245.39   3.808%   $254.7345   $254.73   $254.75   $254.70  
  Purchase #5 $26.81   4.190%   $27.9333   $27.93   $27.95   $27.90  
  Purchase #6 $243.94   11.564%   $272.1492   $272.15   $272.15   $272.10  
  Purchase #7 $69.33   10.423%   $76.5563   $76.56   $76.55   $76.60  
  7 purchase totals = $1,217.06       $1,292.7653   $1,292.75   $1,292.75   $1,292.80