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 $193.61   11.848%   $216.5489   $216.55   $216.55   $216.50  
  Purchase #2 $201.44   13.142%   $227.9132   $227.91   $227.90   $227.90  
  Purchase #3 $98.57   8.697%   $107.1426   $107.14   $107.15   $107.10  
  Purchase #4 $204.35   11.432%   $227.7113   $227.71   $227.70   $227.70  
  Purchase #5 $250.81   5.806%   $265.372   $265.37   $265.35   $265.40  
  Purchase #6 $46.62   6.225%   $49.5221   $49.52   $49.50   $49.50  
  Purchase #7 $125.67   6.737%   $134.1364   $134.14   $134.15   $134.10  
  7 purchase totals = $1,121.07       $1,228.3465   $1,228.34   $1,228.30   $1,228.20