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 $154.26   9.402%   $168.7635   $168.76   $168.75   $168.80  
  Purchase #2 $113.34   3.477%   $117.2808   $117.28   $117.30   $117.30  
  Purchase #3 $26.59   8.631%   $28.885   $28.89   $28.90   $28.90  
  Purchase #4 $141.59   10.489%   $156.4414   $156.44   $156.45   $156.40  
  Purchase #5 $95.25   6.601%   $101.5375   $101.54   $101.55   $101.50  
  Purchase #6 $182.70   8.803%   $198.7831   $198.78   $198.80   $198.80  
  Purchase #7 $171.45   6.623%   $182.8051   $182.81   $182.80   $182.80  
  7 purchase totals = $885.18       $954.4964   $954.50   $954.55   $954.50