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 $60.55   7.365%   $65.0095   $65.01   $65.00   $65.00  
  Purchase #2 $49.65   7.776%   $53.5108   $53.51   $53.50   $53.50  
  Purchase #3 $78.68   3.349%   $81.315   $81.32   $81.30   $81.30  
  Purchase #4 $105.40   13.306%   $119.4245   $119.42   $119.40   $119.40  
  Purchase #5 $65.66   3.474%   $67.941   $67.94   $67.95   $67.90  
  Purchase #6 $244.64   9.522%   $267.9346   $267.93   $267.95   $267.90  
  Purchase #7 $200.83   13.195%   $227.3295   $227.33   $227.35   $227.30  
  7 purchase totals = $805.41       $882.4649   $882.46   $882.45   $882.30