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 $185.97   5.506%   $196.2095   $196.21   $196.20   $196.20  
  Purchase #2 $76.48   4.152%   $79.6554   $79.66   $79.65   $79.70  
  Purchase #3 $153.96   7.135%   $164.945   $164.95   $164.95   $164.90  
  Purchase #4 $176.30   12.290%   $197.9673   $197.97   $197.95   $198.00  
  Purchase #5 $5.30   7.521%   $5.6986   $5.70   $5.70   $5.70  
  Purchase #6 $78.88   4.213%   $82.2032   $82.20   $82.20   $82.20  
  Purchase #7 $179.59   12.826%   $202.6242   $202.62   $202.60   $202.60  
  7 purchase totals = $856.48       $929.3032   $929.31   $929.25   $929.30