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 $235.34   12.488%   $264.7293   $264.73   $264.75   $264.70  
  Purchase #2 $99.74   5.856%   $105.5808   $105.58   $105.60   $105.60  
  Purchase #3 $181.71   12.291%   $204.044   $204.04   $204.05   $204.00  
  Purchase #4 $52.26   7.648%   $56.2568   $56.26   $56.25   $56.30  
  Purchase #5 $33.60   3.238%   $34.688   $34.69   $34.70   $34.70  
  Purchase #6 $196.72   8.839%   $214.1081   $214.11   $214.10   $214.10  
  Purchase #7 $77.82   8.594%   $84.5079   $84.51   $84.50   $84.50  
  7 purchase totals = $877.19       $963.9149   $963.92   $963.95   $963.90