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 $93.58   4.151%   $97.4645   $97.46   $97.45   $97.50  
  Purchase #2 $89.81   5.748%   $94.9723   $94.97   $94.95   $95.00  
  Purchase #3 $107.95   10.870%   $119.6842   $119.68   $119.70   $119.70  
  Purchase #4 $239.91   9.299%   $262.2192   $262.22   $262.20   $262.20  
  Purchase #5 $163.37   8.632%   $177.4721   $177.47   $177.45   $177.50  
  Purchase #6 $98.41   9.648%   $107.9046   $107.90   $107.90   $107.90  
  Purchase #7 $178.62   5.184%   $187.8797   $187.88   $187.90   $187.90  
  7 purchase totals = $971.65       $1,047.5966   $1,047.58   $1,047.55   $1,047.70