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 $205.38   8.816%   $223.4863   $223.49   $223.50   $223.50  
  Purchase #2 $228.57   3.253%   $236.0054   $236.01   $236.00   $236.00  
  Purchase #3 $12.53   7.839%   $13.5122   $13.51   $13.50   $13.50  
  Purchase #4 $63.83   11.863%   $71.4022   $71.40   $71.40   $71.40  
  Purchase #5 $22.79   8.771%   $24.7889   $24.79   $24.80   $24.80  
  Purchase #6 $105.47   8.741%   $114.6891   $114.69   $114.70   $114.70  
  Purchase #7 $249.87   12.113%   $280.1368   $280.14   $280.15   $280.10  
  7 purchase totals = $888.44       $964.0209   $964.03   $964.05   $964.00