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 $233.32   12.662%   $262.863   $262.86   $262.85   $262.90  
  Purchase #2 $223.54   4.857%   $234.3973   $234.40   $234.40   $234.40  
  Purchase #3 $240.80   8.386%   $260.9935   $260.99   $261.00   $261.00  
  Purchase #4 $106.81   8.753%   $116.1591   $116.16   $116.15   $116.20  
  Purchase #5 $57.92   13.308%   $65.628   $65.63   $65.65   $65.60  
  Purchase #6 $154.96   11.802%   $173.2484   $173.25   $173.25   $173.20  
  Purchase #7 $204.67   4.377%   $213.6284   $213.63   $213.65   $213.60  
  7 purchase totals = $1,222.02       $1,326.9177   $1,326.92   $1,326.95   $1,326.90