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 $154.92   6.263%   $164.6226   $164.62   $164.60   $164.60  
  Purchase #2 $199.47   4.443%   $208.3325   $208.33   $208.35   $208.30  
  Purchase #3 $213.44   13.465%   $242.1797   $242.18   $242.20   $242.20  
  Purchase #4 $88.85   7.213%   $95.2588   $95.26   $95.25   $95.30  
  Purchase #5 $140.90   5.821%   $149.1018   $149.10   $149.10   $149.10  
  Purchase #6 $38.53   13.380%   $43.6853   $43.69   $43.70   $43.70  
  Purchase #7 $83.69   10.654%   $92.6063   $92.61   $92.60   $92.60  
  7 purchase totals = $919.80       $995.7870   $995.79   $995.80   $995.80