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 $242.50   10.362%   $267.6279   $267.63   $267.65   $267.60  
  Purchase #2 $157.27   10.291%   $173.4547   $173.45   $173.45   $173.50  
  Purchase #3 $208.85   8.773%   $227.1724   $227.17   $227.15   $227.20  
  Purchase #4 $190.92   13.445%   $216.5892   $216.59   $216.60   $216.60  
  Purchase #5 $110.28   10.447%   $121.801   $121.80   $121.80   $121.80  
  Purchase #6 $196.35   9.482%   $214.9679   $214.97   $214.95   $215.00  
  Purchase #7 $11.26   5.695%   $11.9013   $11.90   $11.90   $11.90  
  7 purchase totals = $1,117.43       $1,233.5144   $1,233.51   $1,233.50   $1,233.60