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 $112.41   10.221%   $123.8994   $123.90   $123.90   $123.90  
  Purchase #2 $151.49   10.851%   $167.9282   $167.93   $167.95   $167.90  
  Purchase #3 $209.43   11.710%   $233.9543   $233.95   $233.95   $234.00  
  Purchase #4 $242.67   3.239%   $250.5301   $250.53   $250.55   $250.50  
  Purchase #5 $92.77   6.315%   $98.6284   $98.63   $98.65   $98.60  
  Purchase #6 $33.31   10.207%   $36.71   $36.71   $36.70   $36.70  
  Purchase #7 $177.55   8.510%   $192.6595   $192.66   $192.65   $192.70  
  7 purchase totals = $1,019.63       $1,104.3099   $1,104.31   $1,104.35   $1,104.30