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 $215.49   9.861%   $236.7395   $236.74   $236.75   $236.70  
  Purchase #2 $213.74   12.765%   $241.0239   $241.02   $241.00   $241.00  
  Purchase #3 $17.31   7.354%   $18.583   $18.58   $18.60   $18.60  
  Purchase #4 $81.35   4.576%   $85.0726   $85.07   $85.05   $85.10  
  Purchase #5 $208.47   8.607%   $226.413   $226.41   $226.40   $226.40  
  Purchase #6 $74.60   10.720%   $82.5971   $82.60   $82.60   $82.60  
  Purchase #7 $11.45   8.584%   $12.4329   $12.43   $12.45   $12.40  
  7 purchase totals = $822.41       $902.8620   $902.85   $902.85   $902.80