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 $243.46   5.278%   $256.3098   $256.31   $256.30   $256.30  
  Purchase #2 $27.69   7.674%   $29.8149   $29.81   $29.80   $29.80  
  Purchase #3 $134.61   3.365%   $139.1396   $139.14   $139.15   $139.10  
  Purchase #4 $112.51   11.418%   $125.3564   $125.36   $125.35   $125.40  
  Purchase #5 $136.59   10.660%   $151.1505   $151.15   $151.15   $151.20  
  Purchase #6 $165.72   10.789%   $183.5995   $183.60   $183.60   $183.60  
  Purchase #7 $176.35   12.628%   $198.6195   $198.62   $198.60   $198.60  
  7 purchase totals = $996.93       $1,083.9902   $1,083.99   $1,083.95   $1,084.00