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 $52.51   13.724%   $59.7165   $59.72   $59.70   $59.70  
  Purchase #2 $95.41   3.495%   $98.7446   $98.74   $98.75   $98.70  
  Purchase #3 $248.87   7.794%   $268.2669   $268.27   $268.25   $268.30  
  Purchase #4 $24.74   5.325%   $26.0574   $26.06   $26.05   $26.10  
  Purchase #5 $205.64   4.196%   $214.2687   $214.27   $214.25   $214.30  
  Purchase #6 $110.35   10.475%   $121.9092   $121.91   $121.90   $121.90  
  Purchase #7 $67.89   4.560%   $70.9858   $70.99   $71.00   $71.00  
  7 purchase totals = $805.41       $859.9491   $859.96   $859.90   $860.00