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 $62.41   5.797%   $66.0279   $66.03   $66.05   $66.00  
  Purchase #2 $51.54   9.358%   $56.3631   $56.36   $56.35   $56.40  
  Purchase #3 $101.62   12.380%   $114.2006   $114.20   $114.20   $114.20  
  Purchase #4 $184.83   9.289%   $201.9989   $202.00   $202.00   $202.00  
  Purchase #5 $33.97   12.329%   $38.1582   $38.16   $38.15   $38.20  
  Purchase #6 $177.48   9.538%   $194.408   $194.41   $194.40   $194.40  
  Purchase #7 $95.44   9.629%   $104.6299   $104.63   $104.65   $104.60  
  7 purchase totals = $707.29       $775.7866   $775.79   $775.80   $775.80