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 $49.42   11.793%   $55.2481   $55.25   $55.25   $55.20  
  Purchase #2 $8.59   5.804%   $9.0886   $9.09   $9.10   $9.10  
  Purchase #3 $69.92   12.312%   $78.5286   $78.53   $78.55   $78.50  
  Purchase #4 $121.96   3.149%   $125.8005   $125.80   $125.80   $125.80  
  Purchase #5 $125.81   11.851%   $140.7197   $140.72   $140.70   $140.70  
  Purchase #6 $188.70   8.863%   $205.4245   $205.42   $205.40   $205.40  
  Purchase #7 $165.83   9.434%   $181.4744   $181.47   $181.45   $181.50  
  7 purchase totals = $730.23       $796.2844   $796.28   $796.25   $796.20