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 $233.90   13.326%   $265.0695   $265.07   $265.05   $265.10  
  Purchase #2 $95.97   7.756%   $103.4134   $103.41   $103.40   $103.40  
  Purchase #3 $130.55   8.669%   $141.8674   $141.87   $141.85   $141.90  
  Purchase #4 $248.44   13.811%   $282.752   $282.75   $282.75   $282.80  
  Purchase #5 $175.98   6.138%   $186.7817   $186.78   $186.80   $186.80  
  Purchase #6 $11.84   12.484%   $13.3181   $13.32   $13.30   $13.30  
  Purchase #7 $155.40   4.618%   $162.5764   $162.58   $162.60   $162.60  
  7 purchase totals = $1,052.08       $1,155.7785   $1,155.78   $1,155.75   $1,155.90