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 $175.39   11.672%   $195.8615   $195.86   $195.85   $195.90  
  Purchase #2 $183.62   7.622%   $197.6155   $197.62   $197.60   $197.60  
  Purchase #3 $200.34   6.665%   $213.6927   $213.69   $213.70   $213.70  
  Purchase #4 $204.25   5.861%   $216.2211   $216.22   $216.20   $216.20  
  Purchase #5 $74.58   12.504%   $83.9055   $83.91   $83.90   $83.90  
  Purchase #6 $7.72   6.455%   $8.2183   $8.22   $8.20   $8.20  
  Purchase #7 $73.25   10.529%   $80.9625   $80.96   $80.95   $81.00  
  7 purchase totals = $919.15       $996.4771   $996.48   $996.40   $996.50