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 $40.55   6.292%   $43.1014   $43.10   $43.10   $43.10  
  Purchase #2 $68.89   6.290%   $73.2232   $73.22   $73.20   $73.20  
  Purchase #3 $71.25   12.297%   $80.0116   $80.01   $80.00   $80.00  
  Purchase #4 $175.48   4.142%   $182.7484   $182.75   $182.75   $182.70  
  Purchase #5 $97.89   3.447%   $101.2643   $101.26   $101.25   $101.30  
  Purchase #6 $250.28   6.692%   $267.0287   $267.03   $267.05   $267.00  
  Purchase #7 $196.29   13.316%   $222.428   $222.43   $222.45   $222.40  
  7 purchase totals = $900.63       $969.8056   $969.80   $969.80   $969.70