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 $175.68   4.595%   $183.7525   $183.75   $183.75   $183.80  
  Purchase #2 $249.61   13.229%   $282.6309   $282.63   $282.65   $282.60  
  Purchase #3 $71.34   6.776%   $76.174   $76.17   $76.15   $76.20  
  Purchase #4 $55.31   3.140%   $57.0467   $57.05   $57.05   $57.00  
  Purchase #5 $95.99   6.795%   $102.5125   $102.51   $102.50   $102.50  
  Purchase #6 $235.95   10.375%   $260.4298   $260.43   $260.45   $260.40  
  Purchase #7 $67.43   4.795%   $70.6633   $70.66   $70.65   $70.70  
  7 purchase totals = $951.31       $1,033.2097   $1,033.20   $1,033.20   $1,033.20