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 $13.68   4.512%   $14.2972   $14.30   $14.30   $14.30  
  Purchase #2 $245.51   6.741%   $262.0598   $262.06   $262.05   $262.10  
  Purchase #3 $214.37   10.802%   $237.5262   $237.53   $237.55   $237.50  
  Purchase #4 $81.81   6.665%   $87.2626   $87.26   $87.25   $87.30  
  Purchase #5 $65.58   12.682%   $73.8969   $73.90   $73.90   $73.90  
  Purchase #6 $144.48   12.845%   $163.0385   $163.04   $163.05   $163.00  
  Purchase #7 $55.87   10.268%   $61.6067   $61.61   $61.60   $61.60  
  7 purchase totals = $821.30       $899.6879   $899.70   $899.70   $899.70