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 $250.44   5.319%   $263.7609   $263.76   $263.75   $263.80  
  Purchase #2 $87.62   11.533%   $97.7252   $97.73   $97.75   $97.70  
  Purchase #3 $164.41   6.437%   $174.9931   $174.99   $175.00   $175.00  
  Purchase #4 $94.33   10.550%   $104.2818   $104.28   $104.30   $104.30  
  Purchase #5 $250.81   4.322%   $261.65   $261.65   $261.65   $261.70  
  Purchase #6 $64.45   13.359%   $73.0599   $73.06   $73.05   $73.10  
  Purchase #7 $156.46   7.720%   $168.5387   $168.54   $168.55   $168.50  
  7 purchase totals = $1,068.52       $1,144.0096   $1,144.01   $1,144.05   $1,144.10