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 $34.73   3.635%   $35.9924   $35.99   $36.00   $36.00  
  Purchase #2 $149.27   11.243%   $166.0524   $166.05   $166.05   $166.10  
  Purchase #3 $19.95   9.298%   $21.805   $21.81   $21.80   $21.80  
  Purchase #4 $250.64   3.524%   $259.4726   $259.47   $259.45   $259.50  
  Purchase #5 $110.90   9.845%   $121.8181   $121.82   $121.80   $121.80  
  Purchase #6 $212.53   10.825%   $235.5364   $235.54   $235.55   $235.50  
  Purchase #7 $157.70   12.610%   $177.586   $177.59   $177.60   $177.60  
  7 purchase totals = $935.72       $1,018.2629   $1,018.27   $1,018.25   $1,018.30