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 $214.25   11.637%   $239.1823   $239.18   $239.20   $239.20  
  Purchase #2 $151.81   8.360%   $164.5013   $164.50   $164.50   $164.50  
  Purchase #3 $176.74   9.423%   $193.3942   $193.39   $193.40   $193.40  
  Purchase #4 $47.42   13.749%   $53.9398   $53.94   $53.95   $53.90  
  Purchase #5 $196.58   11.637%   $219.456   $219.46   $219.45   $219.50  
  Purchase #6 $79.76   10.787%   $88.3637   $88.36   $88.35   $88.40  
  Purchase #7 $60.52   6.759%   $64.6105   $64.61   $64.60   $64.60  
  7 purchase totals = $927.08       $1,023.4478   $1,023.44   $1,023.45   $1,023.50