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 $62.32   5.817%   $65.9452   $65.95   $65.95   $65.90  
  Purchase #2 $38.49   9.577%   $42.1762   $42.18   $42.20   $42.20  
  Purchase #3 $244.95   13.400%   $277.7733   $277.77   $277.75   $277.80  
  Purchase #4 $239.50   10.780%   $265.3181   $265.32   $265.30   $265.30  
  Purchase #5 $162.60   13.853%   $185.125   $185.13   $185.15   $185.10  
  Purchase #6 $79.50   8.821%   $86.5127   $86.51   $86.50   $86.50  
  Purchase #7 $69.69   9.152%   $76.068   $76.07   $76.05   $76.10  
  7 purchase totals = $897.05       $998.9185   $998.93   $998.90   $998.90