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 $228.72   13.688%   $260.0272   $260.03   $260.05   $260.00  
  Purchase #2 $239.51   9.419%   $262.0694   $262.07   $262.05   $262.10  
  Purchase #3 $168.36   4.393%   $175.7561   $175.76   $175.75   $175.80  
  Purchase #4 $53.82   3.645%   $55.7817   $55.78   $55.80   $55.80  
  Purchase #5 $98.87   5.469%   $104.2772   $104.28   $104.30   $104.30  
  Purchase #6 $41.88   12.202%   $46.9902   $46.99   $47.00   $47.00  
  Purchase #7 $128.97   13.799%   $146.7666   $146.77   $146.75   $146.80  
  7 purchase totals = $960.13       $1,051.6684   $1,051.68   $1,051.70   $1,051.80