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 $226.93   12.190%   $254.5928   $254.59   $254.60   $254.60  
  Purchase #2 $164.94   6.767%   $176.1015   $176.10   $176.10   $176.10  
  Purchase #3 $24.77   5.523%   $26.138   $26.14   $26.15   $26.10  
  Purchase #4 $136.38   11.271%   $151.7514   $151.75   $151.75   $151.80  
  Purchase #5 $242.70   7.536%   $260.9899   $260.99   $261.00   $261.00  
  Purchase #6 $155.76   9.791%   $171.0105   $171.01   $171.00   $171.00  
  Purchase #7 $161.37   7.401%   $173.313   $173.31   $173.30   $173.30  
  7 purchase totals = $1,112.85       $1,213.8971   $1,213.89   $1,213.90   $1,213.90