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 $241.39   3.513%   $249.87   $249.87   $249.85   $249.90  
  Purchase #2 $99.35   8.371%   $107.6666   $107.67   $107.65   $107.70  
  Purchase #3 $33.37   13.669%   $37.9313   $37.93   $37.95   $37.90  
  Purchase #4 $190.49   10.285%   $210.0819   $210.08   $210.10   $210.10  
  Purchase #5 $124.47   8.214%   $134.694   $134.69   $134.70   $134.70  
  Purchase #6 $86.75   3.806%   $90.0517   $90.05   $90.05   $90.10  
  Purchase #7 $164.87   5.666%   $174.2115   $174.21   $174.20   $174.20  
  7 purchase totals = $940.69       $1,004.5070   $1,004.50   $1,004.50   $1,004.60