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 $92.29   7.259%   $98.9893   $98.99   $99.00   $99.00  
  Purchase #2 $145.73   10.859%   $161.5548   $161.55   $161.55   $161.60  
  Purchase #3 $126.67   6.203%   $134.5273   $134.53   $134.55   $134.50  
  Purchase #4 $241.72   8.802%   $262.9962   $263.00   $263.00   $263.00  
  Purchase #5 $222.73   10.239%   $245.5353   $245.54   $245.55   $245.50  
  Purchase #6 $114.33   10.696%   $126.5587   $126.56   $126.55   $126.60  
  Purchase #7 $136.25   3.651%   $141.2245   $141.22   $141.20   $141.20  
  7 purchase totals = $1,079.72       $1,171.3861   $1,171.39   $1,171.40   $1,171.40