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 $173.95   4.169%   $181.202   $181.20   $181.20   $181.20  
  Purchase #2 $23.91   11.838%   $26.7405   $26.74   $26.75   $26.70  
  Purchase #3 $154.25   13.162%   $174.5524   $174.55   $174.55   $174.60  
  Purchase #4 $241.72   3.427%   $250.0037   $250.00   $250.00   $250.00  
  Purchase #5 $68.78   5.185%   $72.3462   $72.35   $72.35   $72.30  
  Purchase #6 $68.76   6.806%   $73.4398   $73.44   $73.45   $73.40  
  Purchase #7 $161.32   7.294%   $173.0867   $173.09   $173.10   $173.10  
  7 purchase totals = $892.69       $951.3713   $951.37   $951.40   $951.30