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 $248.64   6.407%   $264.5704   $264.57   $264.55   $264.60  
  Purchase #2 $131.99   13.348%   $149.608   $149.61   $149.60   $149.60  
  Purchase #3 $34.76   3.106%   $35.8396   $35.84   $35.85   $35.80  
  Purchase #4 $76.70   7.824%   $82.701   $82.70   $82.70   $82.70  
  Purchase #5 $172.73   11.821%   $193.1484   $193.15   $193.15   $193.10  
  Purchase #6 $13.48   10.625%   $14.9123   $14.91   $14.90   $14.90  
  Purchase #7 $207.63   9.129%   $226.5845   $226.58   $226.60   $226.60  
  7 purchase totals = $885.93       $967.3642   $967.36   $967.35   $967.30