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 $9.51   4.558%   $9.9435   $9.94   $9.95   $9.90  
  Purchase #2 $136.99   4.434%   $143.0641   $143.06   $143.05   $143.10  
  Purchase #3 $186.59   7.387%   $200.3734   $200.37   $200.35   $200.40  
  Purchase #4 $10.85   13.490%   $12.3137   $12.31   $12.30   $12.30  
  Purchase #5 $187.67   7.656%   $202.038   $202.04   $202.05   $202.00  
  Purchase #6 $208.44   4.684%   $218.2033   $218.20   $218.20   $218.20  
  Purchase #7 $158.68   13.746%   $180.4922   $180.49   $180.50   $180.50  
  7 purchase totals = $898.73       $966.4282   $966.41   $966.40   $966.40