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 $238.39   11.862%   $266.6678   $266.67   $266.65   $266.70  
  Purchase #2 $12.48   3.342%   $12.8971   $12.90   $12.90   $12.90  
  Purchase #3 $242.89   12.427%   $273.0739   $273.07   $273.05   $273.10  
  Purchase #4 $32.74   4.786%   $34.3069   $34.31   $34.30   $34.30  
  Purchase #5 $131.46   8.758%   $142.9733   $142.97   $142.95   $143.00  
  Purchase #6 $58.29   13.110%   $65.9318   $65.93   $65.95   $65.90  
  Purchase #7 $202.79   5.225%   $213.3858   $213.39   $213.40   $213.40  
  7 purchase totals = $919.04       $1,009.2366   $1,009.24   $1,009.20   $1,009.30