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 $101.57   6.595%   $108.2685   $108.27   $108.25   $108.30  
  Purchase #2 $201.49   13.148%   $227.9819   $227.98   $228.00   $228.00  
  Purchase #3 $224.40   5.121%   $235.8915   $235.89   $235.90   $235.90  
  Purchase #4 $58.40   7.312%   $62.6702   $62.67   $62.65   $62.70  
  Purchase #5 $234.48   13.455%   $266.0293   $266.03   $266.05   $266.00  
  Purchase #6 $192.63   3.661%   $199.6822   $199.68   $199.70   $199.70  
  Purchase #7 $177.61   10.473%   $196.2111   $196.21   $196.20   $196.20  
  7 purchase totals = $1,190.58       $1,296.7347   $1,296.73   $1,296.75   $1,296.80