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 $235.61   10.834%   $261.136   $261.14   $261.15   $261.10  
  Purchase #2 $9.26   9.653%   $10.1539   $10.15   $10.15   $10.20  
  Purchase #3 $57.36   8.351%   $62.1501   $62.15   $62.15   $62.20  
  Purchase #4 $227.31   8.619%   $246.9018   $246.90   $246.90   $246.90  
  Purchase #5 $47.37   13.373%   $53.7048   $53.70   $53.70   $53.70  
  Purchase #6 $159.59   3.318%   $164.8852   $164.89   $164.90   $164.90  
  Purchase #7 $120.25   5.633%   $127.0237   $127.02   $127.00   $127.00  
  7 purchase totals = $856.75       $925.9555   $925.95   $925.95   $926.00