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 $146.92   8.360%   $159.2025   $159.20   $159.20   $159.20  
  Purchase #2 $59.83   8.184%   $64.7265   $64.73   $64.75   $64.70  
  Purchase #3 $174.92   4.484%   $182.7634   $182.76   $182.75   $182.80  
  Purchase #4 $33.69   4.105%   $35.073   $35.07   $35.05   $35.10  
  Purchase #5 $242.39   12.691%   $273.1517   $273.15   $273.15   $273.20  
  Purchase #6 $213.94   10.384%   $236.1555   $236.16   $236.15   $236.20  
  Purchase #7 $119.50   9.406%   $130.7402   $130.74   $130.75   $130.70  
  7 purchase totals = $991.19       $1,081.8128   $1,081.81   $1,081.80   $1,081.90