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 $43.83   12.242%   $49.1957   $49.20   $49.20   $49.20  
  Purchase #2 $162.79   11.722%   $181.8722   $181.87   $181.85   $181.90  
  Purchase #3 $86.84   12.630%   $97.8079   $97.81   $97.80   $97.80  
  Purchase #4 $47.97   5.437%   $50.5781   $50.58   $50.60   $50.60  
  Purchase #5 $250.95   3.715%   $260.2728   $260.27   $260.25   $260.30  
  Purchase #6 $245.76   13.763%   $279.5839   $279.58   $279.60   $279.60  
  Purchase #7 $157.48   4.511%   $164.5839   $164.58   $164.60   $164.60  
  7 purchase totals = $995.62       $1,083.8945   $1,083.89   $1,083.90   $1,084.00