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 $224.82   13.288%   $254.6941   $254.69   $254.70   $254.70  
  Purchase #2 $247.74   5.387%   $261.0858   $261.09   $261.10   $261.10  
  Purchase #3 $114.25   11.116%   $126.95   $126.95   $126.95   $127.00  
  Purchase #4 $115.45   9.627%   $126.5644   $126.56   $126.55   $126.60  
  Purchase #5 $102.40   5.520%   $108.0525   $108.05   $108.05   $108.10  
  Purchase #6 $88.81   4.308%   $92.6359   $92.64   $92.65   $92.60  
  Purchase #7 $61.69   5.117%   $64.8467   $64.85   $64.85   $64.80  
  7 purchase totals = $955.16       $1,034.8294   $1,034.83   $1,034.85   $1,034.90