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 $79.90   4.189%   $83.247   $83.25   $83.25   $83.20  
  Purchase #2 $226.45   10.518%   $250.268   $250.27   $250.25   $250.30  
  Purchase #3 $164.59   6.589%   $175.4348   $175.43   $175.45   $175.40  
  Purchase #4 $154.39   8.133%   $166.9465   $166.95   $166.95   $166.90  
  Purchase #5 $69.88   8.556%   $75.8589   $75.86   $75.85   $75.90  
  Purchase #6 $140.55   3.221%   $145.0771   $145.08   $145.10   $145.10  
  Purchase #7 $36.60   4.249%   $38.1551   $38.16   $38.15   $38.20  
  7 purchase totals = $872.36       $934.9874   $935.00   $935.00   $935.00