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 $248.42   3.176%   $256.3098   $256.31   $256.30   $256.30  
  Purchase #2 $236.73   11.518%   $263.9966   $264.00   $264.00   $264.00  
  Purchase #3 $104.35   12.706%   $117.6087   $117.61   $117.60   $117.60  
  Purchase #4 $35.94   6.678%   $38.3401   $38.34   $38.35   $38.30  
  Purchase #5 $32.67   7.260%   $35.0418   $35.04   $35.05   $35.00  
  Purchase #6 $246.44   10.600%   $272.5626   $272.56   $272.55   $272.60  
  Purchase #7 $42.28   5.764%   $44.717   $44.72   $44.70   $44.70  
  7 purchase totals = $946.83       $1,028.5766   $1,028.58   $1,028.55   $1,028.50