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 $216.62   11.787%   $242.153   $242.15   $242.15   $242.20  
  Purchase #2 $82.59   12.146%   $92.6214   $92.62   $92.60   $92.60  
  Purchase #3 $183.80   13.281%   $208.2105   $208.21   $208.20   $208.20  
  Purchase #4 $77.36   7.737%   $83.3453   $83.35   $83.35   $83.30  
  Purchase #5 $157.76   12.873%   $178.0684   $178.07   $178.05   $178.10  
  Purchase #6 $133.64   10.366%   $147.4931   $147.49   $147.50   $147.50  
  Purchase #7 $30.63   11.656%   $34.2002   $34.20   $34.20   $34.20  
  7 purchase totals = $882.40       $986.0919   $986.09   $986.05   $986.10