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 $146.96   10.380%   $162.2144   $162.21   $162.20   $162.20  
  Purchase #2 $97.46   12.509%   $109.6513   $109.65   $109.65   $109.70  
  Purchase #3 $241.48   12.357%   $271.3197   $271.32   $271.30   $271.30  
  Purchase #4 $223.36   13.470%   $253.4466   $253.45   $253.45   $253.40  
  Purchase #5 $109.26   4.430%   $114.1002   $114.10   $114.10   $114.10  
  Purchase #6 $236.60   11.531%   $263.8823   $263.88   $263.90   $263.90  
  Purchase #7 $47.62   9.845%   $52.3082   $52.31   $52.30   $52.30  
  7 purchase totals = $1,102.74       $1,226.9227   $1,226.92   $1,226.90   $1,226.90