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 $246.38   6.191%   $261.6334   $261.63   $261.65   $261.60  
  Purchase #2 $76.79   12.488%   $86.3795   $86.38   $86.40   $86.40  
  Purchase #3 $149.36   9.744%   $163.9136   $163.91   $163.90   $163.90  
  Purchase #4 $116.38   4.353%   $121.446   $121.45   $121.45   $121.40  
  Purchase #5 $48.71   7.785%   $52.5021   $52.50   $52.50   $52.50  
  Purchase #6 $80.30   13.361%   $91.0289   $91.03   $91.05   $91.00  
  Purchase #7 $8.33   6.537%   $8.8745   $8.87   $8.85   $8.90  
  7 purchase totals = $726.25       $785.7780   $785.77   $785.80   $785.70