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 $240.29   8.742%   $261.2962   $261.30   $261.30   $261.30  
  Purchase #2 $156.39   6.582%   $166.6836   $166.68   $166.70   $166.70  
  Purchase #3 $26.74   13.114%   $30.2467   $30.25   $30.25   $30.20  
  Purchase #4 $182.59   10.388%   $201.5574   $201.56   $201.55   $201.60  
  Purchase #5 $135.25   8.418%   $146.6353   $146.64   $146.65   $146.60  
  Purchase #6 $71.60   8.696%   $77.8263   $77.83   $77.85   $77.80  
  Purchase #7 $95.39   5.610%   $100.7414   $100.74   $100.75   $100.70  
  7 purchase totals = $908.25       $984.9869   $985.00   $985.05   $984.90