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 $206.88   6.192%   $219.69   $219.69   $219.70   $219.70  
  Purchase #2 $166.49   4.724%   $174.355   $174.36   $174.35   $174.40  
  Purchase #3 $97.45   7.367%   $104.6291   $104.63   $104.65   $104.60  
  Purchase #4 $190.88   6.334%   $202.9703   $202.97   $202.95   $203.00  
  Purchase #5 $79.26   3.249%   $81.8352   $81.84   $81.85   $81.80  
  Purchase #6 $42.53   10.823%   $47.133   $47.13   $47.15   $47.10  
  Purchase #7 $72.99   4.467%   $76.2505   $76.25   $76.25   $76.30  
  7 purchase totals = $856.48       $906.8631   $906.87   $906.90   $906.90