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 $186.31   9.465%   $203.9442   $203.94   $203.95   $203.90  
  Purchase #2 $136.92   8.568%   $148.6513   $148.65   $148.65   $148.70  
  Purchase #3 $116.61   5.414%   $122.9233   $122.92   $122.90   $122.90  
  Purchase #4 $221.30   7.634%   $238.194   $238.19   $238.20   $238.20  
  Purchase #5 $121.79   12.697%   $137.2537   $137.25   $137.25   $137.30  
  Purchase #6 $218.89   5.733%   $231.439   $231.44   $231.45   $231.40  
  Purchase #7 $21.54   7.730%   $23.205   $23.21   $23.20   $23.20  
  7 purchase totals = $1,023.36       $1,105.6105   $1,105.60   $1,105.60   $1,105.60