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 $86.64   7.655%   $93.2723   $93.27   $93.25   $93.30  
  Purchase #2 $114.47   8.872%   $124.6258   $124.63   $124.65   $124.60  
  Purchase #3 $248.49   4.405%   $259.436   $259.44   $259.45   $259.40  
  Purchase #4 $98.72   6.345%   $104.9838   $104.98   $105.00   $105.00  
  Purchase #5 $208.34   13.627%   $236.7305   $236.73   $236.75   $236.70  
  Purchase #6 $45.57   4.305%   $47.5318   $47.53   $47.55   $47.50  
  Purchase #7 $139.45   3.404%   $144.1969   $144.20   $144.20   $144.20  
  7 purchase totals = $941.68       $1,010.7771   $1,010.78   $1,010.85   $1,010.70