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 $58.45   13.329%   $66.2408   $66.24   $66.25   $66.20  
  Purchase #2 $100.54   7.300%   $107.8794   $107.88   $107.90   $107.90  
  Purchase #3 $126.78   8.402%   $137.4321   $137.43   $137.45   $137.40  
  Purchase #4 $226.99   12.838%   $256.131   $256.13   $256.15   $256.10  
  Purchase #5 $174.31   9.719%   $191.2512   $191.25   $191.25   $191.30  
  Purchase #6 $238.84   9.362%   $261.2002   $261.20   $261.20   $261.20  
  Purchase #7 $155.41   13.682%   $176.6732   $176.67   $176.65   $176.70  
  7 purchase totals = $1,081.32       $1,196.8079   $1,196.80   $1,196.85   $1,196.80