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 $59.95   10.477%   $66.231   $66.23   $66.25   $66.20  
  Purchase #2 $235.61   6.764%   $251.5467   $251.55   $251.55   $251.50  
  Purchase #3 $14.82   12.788%   $16.7152   $16.72   $16.70   $16.70  
  Purchase #4 $47.32   13.273%   $53.6008   $53.60   $53.60   $53.60  
  Purchase #5 $106.55   10.795%   $118.0521   $118.05   $118.05   $118.10  
  Purchase #6 $175.88   5.868%   $186.2006   $186.20   $186.20   $186.20  
  Purchase #7 $245.59   8.401%   $266.222   $266.22   $266.20   $266.20  
  7 purchase totals = $885.72       $958.5684   $958.57   $958.55   $958.50