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 $159.48   5.790%   $168.7139   $168.71   $168.70   $168.70  
  Purchase #2 $46.28   11.236%   $51.48   $51.48   $51.50   $51.50  
  Purchase #3 $34.99   4.682%   $36.6282   $36.63   $36.65   $36.60  
  Purchase #4 $226.89   8.527%   $246.2369   $246.24   $246.25   $246.20  
  Purchase #5 $212.68   11.802%   $237.7805   $237.78   $237.80   $237.80  
  Purchase #6 $56.28   6.565%   $59.9748   $59.97   $59.95   $60.00  
  Purchase #7 $121.67   3.558%   $125.999   $126.00   $126.00   $126.00  
  7 purchase totals = $858.27       $926.8133   $926.81   $926.85   $926.80