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 $176.68   12.696%   $199.1113   $199.11   $199.10   $199.10  
  Purchase #2 $233.75   8.461%   $253.5276   $253.53   $253.55   $253.50  
  Purchase #3 $242.48   7.845%   $261.5026   $261.50   $261.50   $261.50  
  Purchase #4 $158.29   13.418%   $179.5294   $179.53   $179.55   $179.50  
  Purchase #5 $23.61   11.492%   $26.3233   $26.32   $26.30   $26.30  
  Purchase #6 $30.59   8.718%   $33.2568   $33.26   $33.25   $33.30  
  Purchase #7 $212.40   9.115%   $231.7603   $231.76   $231.75   $231.80  
  7 purchase totals = $1,077.80       $1,185.0113   $1,185.01   $1,185.00   $1,185.00