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 $70.69   8.510%   $76.7057   $76.71   $76.70   $76.70  
  Purchase #2 $239.33   3.432%   $247.5438   $247.54   $247.55   $247.50  
  Purchase #3 $158.98   3.467%   $164.4918   $164.49   $164.50   $164.50  
  Purchase #4 $71.72   8.809%   $78.0378   $78.04   $78.05   $78.00  
  Purchase #5 $51.63   8.752%   $56.1487   $56.15   $56.15   $56.10  
  Purchase #6 $13.29   4.652%   $13.9083   $13.91   $13.90   $13.90  
  Purchase #7 $146.83   8.415%   $159.1857   $159.19   $159.20   $159.20  
  7 purchase totals = $752.47       $796.0218   $796.03   $796.05   $795.90