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 $248.26   5.150%   $261.0454   $261.05   $261.05   $261.00  
  Purchase #2 $87.28   12.821%   $98.4702   $98.47   $98.45   $98.50  
  Purchase #3 $146.41   13.425%   $166.0655   $166.07   $166.05   $166.10  
  Purchase #4 $22.53   8.750%   $24.5014   $24.50   $24.50   $24.50  
  Purchase #5 $211.27   5.423%   $222.7272   $222.73   $222.75   $222.70  
  Purchase #6 $28.31   8.353%   $30.6747   $30.67   $30.65   $30.70  
  Purchase #7 $225.64   11.838%   $252.3513   $252.35   $252.35   $252.40  
  7 purchase totals = $969.70       $1,055.8357   $1,055.84   $1,055.80   $1,055.90