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 $219.43   6.554%   $233.8114   $233.81   $233.80   $233.80  
  Purchase #2 $187.52   4.627%   $196.1966   $196.20   $196.20   $196.20  
  Purchase #3 $77.68   10.622%   $85.9312   $85.93   $85.95   $85.90  
  Purchase #4 $170.64   13.130%   $193.045   $193.05   $193.05   $193.00  
  Purchase #5 $134.85   12.167%   $151.2572   $151.26   $151.25   $151.30  
  Purchase #6 $236.73   4.591%   $247.5983   $247.60   $247.60   $247.60  
  Purchase #7 $240.69   8.496%   $261.139   $261.14   $261.15   $261.10  
  7 purchase totals = $1,267.54       $1,368.9787   $1,368.99   $1,369.00   $1,368.90