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 $55.93   6.550%   $59.5934   $59.59   $59.60   $59.60  
  Purchase #2 $214.81   12.387%   $241.4185   $241.42   $241.40   $241.40  
  Purchase #3 $111.88   5.806%   $118.3758   $118.38   $118.40   $118.40  
  Purchase #4 $129.64   6.114%   $137.5662   $137.57   $137.55   $137.60  
  Purchase #5 $74.86   6.115%   $79.4377   $79.44   $79.45   $79.40  
  Purchase #6 $90.86   12.170%   $101.9177   $101.92   $101.90   $101.90  
  Purchase #7 $185.26   4.241%   $193.1169   $193.12   $193.10   $193.10  
  7 purchase totals = $863.24       $931.4262   $931.44   $931.40   $931.40