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 $218.60   9.456%   $239.2708   $239.27   $239.25   $239.30  
  Purchase #2 $104.67   13.323%   $118.6152   $118.62   $118.60   $118.60  
  Purchase #3 $106.66   6.849%   $113.9651   $113.97   $113.95   $114.00  
  Purchase #4 $25.46   11.327%   $28.3439   $28.34   $28.35   $28.30  
  Purchase #5 $60.94   7.592%   $65.5666   $65.57   $65.55   $65.60  
  Purchase #6 $50.66   4.418%   $52.8982   $52.90   $52.90   $52.90  
  Purchase #7 $151.51   7.865%   $163.4263   $163.43   $163.45   $163.40  
  7 purchase totals = $718.50       $782.0861   $782.10   $782.05   $782.10