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 $208.46   5.603%   $220.14   $220.14   $220.15   $220.10  
  Purchase #2 $18.27   10.284%   $20.1489   $20.15   $20.15   $20.10  
  Purchase #3 $181.64   6.803%   $193.997   $194.00   $194.00   $194.00  
  Purchase #4 $244.71   6.802%   $261.3552   $261.36   $261.35   $261.40  
  Purchase #5 $54.32   11.577%   $60.6086   $60.61   $60.60   $60.60  
  Purchase #6 $226.72   11.590%   $252.9968   $253.00   $253.00   $253.00  
  Purchase #7 $241.38   8.314%   $261.4483   $261.45   $261.45   $261.40  
  7 purchase totals = $1,175.50       $1,270.6948   $1,270.71   $1,270.70   $1,270.60