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 $58.84   6.182%   $62.4775   $62.48   $62.50   $62.50  
  Purchase #2 $248.91   5.173%   $261.7861   $261.79   $261.80   $261.80  
  Purchase #3 $33.61   8.359%   $36.4195   $36.42   $36.40   $36.40  
  Purchase #4 $140.48   5.672%   $148.448   $148.45   $148.45   $148.40  
  Purchase #5 $66.27   3.626%   $68.673   $68.67   $68.65   $68.70  
  Purchase #6 $121.34   11.719%   $135.5598   $135.56   $135.55   $135.60  
  Purchase #7 $167.53   12.714%   $188.8298   $188.83   $188.85   $188.80  
  7 purchase totals = $836.98       $902.1937   $902.20   $902.20   $902.20