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 $146.69   13.665%   $166.7352   $166.74   $166.75   $166.70  
  Purchase #2 $232.60   9.153%   $253.8899   $253.89   $253.90   $253.90  
  Purchase #3 $157.93   3.243%   $163.0517   $163.05   $163.05   $163.10  
  Purchase #4 $43.60   9.783%   $47.8654   $47.87   $47.85   $47.90  
  Purchase #5 $185.66   3.333%   $191.848   $191.85   $191.85   $191.80  
  Purchase #6 $174.58   10.521%   $192.9476   $192.95   $192.95   $192.90  
  Purchase #7 $56.79   13.326%   $64.3578   $64.36   $64.35   $64.40  
  7 purchase totals = $997.85       $1,080.6956   $1,080.71   $1,080.70   $1,080.70