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 $95.77   11.403%   $106.6907   $106.69   $106.70   $106.70  
  Purchase #2 $103.39   9.230%   $112.9329   $112.93   $112.95   $112.90  
  Purchase #3 $216.89   5.117%   $227.9883   $227.99   $228.00   $228.00  
  Purchase #4 $41.93   13.508%   $47.5939   $47.59   $47.60   $47.60  
  Purchase #5 $208.37   13.230%   $235.9374   $235.94   $235.95   $235.90  
  Purchase #6 $52.28   6.713%   $55.7896   $55.79   $55.80   $55.80  
  Purchase #7 $124.88   6.227%   $132.6563   $132.66   $132.65   $132.70  
  7 purchase totals = $843.51       $919.5891   $919.59   $919.65   $919.60