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 $6.59   4.525%   $6.8882   $6.89   $6.90   $6.90  
  Purchase #2 $149.49   13.169%   $169.1763   $169.18   $169.20   $169.20  
  Purchase #3 $104.57   9.538%   $114.5439   $114.54   $114.55   $114.50  
  Purchase #4 $104.81   4.808%   $109.8493   $109.85   $109.85   $109.80  
  Purchase #5 $222.44   8.860%   $242.1482   $242.15   $242.15   $242.10  
  Purchase #6 $161.97   5.615%   $171.0646   $171.06   $171.05   $171.10  
  Purchase #7 $67.62   10.213%   $74.526   $74.53   $74.55   $74.50  
  7 purchase totals = $817.49       $888.1965   $888.20   $888.25   $888.10