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 $67.59   10.262%   $74.5261   $74.53   $74.55   $74.50  
  Purchase #2 $46.94   11.662%   $52.4141   $52.41   $52.40   $52.40  
  Purchase #3 $168.63   8.199%   $182.456   $182.46   $182.45   $182.50  
  Purchase #4 $160.71   9.567%   $176.0851   $176.09   $176.10   $176.10  
  Purchase #5 $77.84   10.815%   $86.2584   $86.26   $86.25   $86.30  
  Purchase #6 $165.51   4.806%   $173.4644   $173.46   $173.45   $173.50  
  Purchase #7 $49.85   6.464%   $53.0723   $53.07   $53.05   $53.10  
  7 purchase totals = $737.07       $798.2764   $798.28   $798.25   $798.40