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 $101.45   12.569%   $114.2013   $114.20   $114.20   $114.20  
  Purchase #2 $140.35   10.195%   $154.6587   $154.66   $154.65   $154.70  
  Purchase #3 $83.75   6.331%   $89.0522   $89.05   $89.05   $89.10  
  Purchase #4 $183.90   8.565%   $199.651   $199.65   $199.65   $199.70  
  Purchase #5 $158.97   12.237%   $178.4232   $178.42   $178.40   $178.40  
  Purchase #6 $13.57   5.816%   $14.3592   $14.36   $14.35   $14.40  
  Purchase #7 $132.72   7.144%   $142.2015   $142.20   $142.20   $142.20  
  7 purchase totals = $814.71       $892.5471   $892.54   $892.50   $892.70