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 $53.80   13.463%   $61.0431   $61.04   $61.05   $61.00  
  Purchase #2 $176.48   9.856%   $193.8739   $193.87   $193.85   $193.90  
  Purchase #3 $168.63   8.750%   $183.3851   $183.39   $183.40   $183.40  
  Purchase #4 $102.68   9.776%   $112.718   $112.72   $112.70   $112.70  
  Purchase #5 $142.47   13.838%   $162.185   $162.19   $162.20   $162.20  
  Purchase #6 $235.33   8.727%   $255.8672   $255.87   $255.85   $255.90  
  Purchase #7 $237.32   12.797%   $267.6898   $267.69   $267.70   $267.70  
  7 purchase totals = $1,116.71       $1,236.7621   $1,236.77   $1,236.75   $1,236.80