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 $247.83   4.537%   $259.074   $259.07   $259.05   $259.10  
  Purchase #2 $85.58   11.874%   $95.7418   $95.74   $95.75   $95.70  
  Purchase #3 $8.45   13.477%   $9.5888   $9.59   $9.60   $9.60  
  Purchase #4 $131.25   8.531%   $142.4469   $142.45   $142.45   $142.40  
  Purchase #5 $79.66   8.502%   $86.4327   $86.43   $86.45   $86.40  
  Purchase #6 $228.91   11.653%   $255.5849   $255.58   $255.60   $255.60  
  Purchase #7 $214.34   10.541%   $236.9336   $236.93   $236.95   $236.90  
  7 purchase totals = $996.02       $1,085.8027   $1,085.79   $1,085.85   $1,085.70