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 $32.62   3.260%   $33.6834   $33.68   $33.70   $33.70  
  Purchase #2 $170.25   9.640%   $186.6621   $186.66   $186.65   $186.70  
  Purchase #3 $180.73   4.443%   $188.7598   $188.76   $188.75   $188.80  
  Purchase #4 $233.31   11.526%   $260.2013   $260.20   $260.20   $260.20  
  Purchase #5 $52.32   8.198%   $56.6092   $56.61   $56.60   $56.60  
  Purchase #6 $66.27   7.343%   $71.1362   $71.14   $71.15   $71.10  
  Purchase #7 $218.65   4.543%   $228.5833   $228.58   $228.60   $228.60  
  7 purchase totals = $954.15       $1,025.6353   $1,025.63   $1,025.65   $1,025.70