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 $204.86   4.639%   $214.3635   $214.36   $214.35   $214.40  
  Purchase #2 $217.51   11.697%   $242.9521   $242.95   $242.95   $243.00  
  Purchase #3 $69.49   12.242%   $77.997   $78.00   $78.00   $78.00  
  Purchase #4 $78.27   4.407%   $81.7194   $81.72   $81.70   $81.70  
  Purchase #5 $106.80   8.532%   $115.9122   $115.91   $115.90   $115.90  
  Purchase #6 $9.81   6.706%   $10.4679   $10.47   $10.45   $10.50  
  Purchase #7 $156.89   7.781%   $169.0976   $169.10   $169.10   $169.10  
  7 purchase totals = $843.63       $912.5097   $912.51   $912.45   $912.60