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 $156.86   8.326%   $169.9202   $169.92   $169.90   $169.90  
  Purchase #2 $22.63   7.191%   $24.2573   $24.26   $24.25   $24.30  
  Purchase #3 $27.80   3.821%   $28.8622   $28.86   $28.85   $28.90  
  Purchase #4 $186.92   11.576%   $208.5579   $208.56   $208.55   $208.60  
  Purchase #5 $38.65   6.195%   $41.0444   $41.04   $41.05   $41.00  
  Purchase #6 $33.35   6.724%   $35.5925   $35.59   $35.60   $35.60  
  Purchase #7 $216.28   3.426%   $223.6898   $223.69   $223.70   $223.70  
  7 purchase totals = $682.49       $731.9243   $731.92   $731.90   $732.00