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 $213.38   13.247%   $241.6464   $241.65   $241.65   $241.60  
  Purchase #2 $77.57   10.165%   $85.455   $85.46   $85.45   $85.50  
  Purchase #3 $48.84   4.617%   $51.0949   $51.09   $51.10   $51.10  
  Purchase #4 $61.45   13.362%   $69.6609   $69.66   $69.65   $69.70  
  Purchase #5 $224.44   7.772%   $241.8835   $241.88   $241.90   $241.90  
  Purchase #6 $172.27   3.874%   $178.9437   $178.94   $178.95   $178.90  
  Purchase #7 $9.35   3.827%   $9.7078   $9.71   $9.70   $9.70  
  7 purchase totals = $807.30       $878.3922   $878.39   $878.40   $878.40