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 $92.44   13.247%   $104.6855   $104.69   $104.70   $104.70  
  Purchase #2 $228.63   10.856%   $253.4501   $253.45   $253.45   $253.50  
  Purchase #3 $207.39   9.271%   $226.6171   $226.62   $226.60   $226.60  
  Purchase #4 $49.88   8.711%   $54.225   $54.23   $54.25   $54.20  
  Purchase #5 $127.91   11.533%   $142.6619   $142.66   $142.65   $142.70  
  Purchase #6 $131.41   6.510%   $139.9648   $139.96   $139.95   $140.00  
  Purchase #7 $244.75   9.254%   $267.3992   $267.40   $267.40   $267.40  
  7 purchase totals = $1,082.41       $1,189.0036   $1,189.01   $1,189.00   $1,189.10