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 $71.51   6.669%   $76.279   $76.28   $76.30   $76.30  
  Purchase #2 $26.68   13.719%   $30.3402   $30.34   $30.35   $30.30  
  Purchase #3 $136.93   11.667%   $152.9056   $152.91   $152.90   $152.90  
  Purchase #4 $217.86   8.368%   $236.0905   $236.09   $236.10   $236.10  
  Purchase #5 $246.68   5.651%   $260.6199   $260.62   $260.60   $260.60  
  Purchase #6 $235.75   5.556%   $248.8483   $248.85   $248.85   $248.80  
  Purchase #7 $74.64   8.786%   $81.1979   $81.20   $81.20   $81.20  
  7 purchase totals = $1,010.05       $1,086.2814   $1,086.29   $1,086.30   $1,086.20