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 $56.74   8.617%   $61.6293   $61.63   $61.65   $61.60  
  Purchase #2 $190.37   12.588%   $214.3338   $214.33   $214.35   $214.30  
  Purchase #3 $88.37   11.622%   $98.6404   $98.64   $98.65   $98.60  
  Purchase #4 $135.65   5.616%   $143.2681   $143.27   $143.25   $143.30  
  Purchase #5 $83.70   3.812%   $86.8906   $86.89   $86.90   $86.90  
  Purchase #6 $94.32   3.259%   $97.3939   $97.39   $97.40   $97.40  
  Purchase #7 $126.53   3.509%   $130.9699   $130.97   $130.95   $131.00  
  7 purchase totals = $775.68       $833.1260   $833.12   $833.15   $833.10