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 $222.57   11.230%   $247.5646   $247.56   $247.55   $247.60  
  Purchase #2 $191.66   8.630%   $208.2003   $208.20   $208.20   $208.20  
  Purchase #3 $42.56   10.440%   $47.0033   $47.00   $47.00   $47.00  
  Purchase #4 $247.42   7.370%   $265.6549   $265.65   $265.65   $265.70  
  Purchase #5 $244.31   13.257%   $276.6982   $276.70   $276.70   $276.70  
  Purchase #6 $89.63   11.287%   $99.7465   $99.75   $99.75   $99.70  
  Purchase #7 $15.83   11.400%   $17.6346   $17.63   $17.65   $17.60  
  7 purchase totals = $1,053.98       $1,162.5024   $1,162.49   $1,162.50   $1,162.50