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 $236.70   10.638%   $261.8801   $261.88   $261.90   $261.90  
  Purchase #2 $188.71   9.657%   $206.9337   $206.93   $206.95   $206.90  
  Purchase #3 $60.59   13.858%   $68.9866   $68.99   $69.00   $69.00  
  Purchase #4 $60.78   5.826%   $64.321   $64.32   $64.30   $64.30  
  Purchase #5 $178.85   5.336%   $188.3934   $188.39   $188.40   $188.40  
  Purchase #6 $86.58   4.635%   $90.593   $90.59   $90.60   $90.60  
  Purchase #7 $174.25   13.556%   $197.8713   $197.87   $197.85   $197.90  
  7 purchase totals = $986.46       $1,078.9791   $1,078.97   $1,079.00   $1,079.00