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 $82.59   4.439%   $86.2562   $86.26   $86.25   $86.30  
  Purchase #2 $114.58   9.696%   $125.6897   $125.69   $125.70   $125.70  
  Purchase #3 $157.75   10.132%   $173.7332   $173.73   $173.75   $173.70  
  Purchase #4 $86.58   6.325%   $92.0562   $92.06   $92.05   $92.10  
  Purchase #5 $123.66   3.373%   $127.8311   $127.83   $127.85   $127.80  
  Purchase #6 $236.80   10.110%   $260.7405   $260.74   $260.75   $260.70  
  Purchase #7 $93.77   5.200%   $98.646   $98.65   $98.65   $98.60  
  7 purchase totals = $895.73       $964.9529   $964.96   $965.00   $964.90