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 $65.99   11.104%   $73.3175   $73.32   $73.30   $73.30  
  Purchase #2 $183.84   9.808%   $201.871   $201.87   $201.85   $201.90  
  Purchase #3 $58.53   3.686%   $60.6874   $60.69   $60.70   $60.70  
  Purchase #4 $177.78   8.866%   $193.542   $193.54   $193.55   $193.50  
  Purchase #5 $101.78   5.786%   $107.669   $107.67   $107.65   $107.70  
  Purchase #6 $96.38   8.545%   $104.6157   $104.62   $104.60   $104.60  
  Purchase #7 $8.76   4.362%   $9.1421   $9.14   $9.15   $9.10  
  7 purchase totals = $693.06       $750.8447   $750.85   $750.80   $750.80