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 $236.91   10.541%   $261.8827   $261.88   $261.90   $261.90  
  Purchase #2 $130.81   10.770%   $144.8982   $144.90   $144.90   $144.90  
  Purchase #3 $94.55   9.382%   $103.4207   $103.42   $103.40   $103.40  
  Purchase #4 $242.50   7.578%   $260.8767   $260.88   $260.90   $260.90  
  Purchase #5 $168.57   4.716%   $176.5198   $176.52   $176.50   $176.50  
  Purchase #6 $193.30   12.456%   $217.3774   $217.38   $217.40   $217.40  
  Purchase #7 $201.65   3.593%   $208.8953   $208.90   $208.90   $208.90  
  7 purchase totals = $1,268.29       $1,373.8708   $1,373.88   $1,373.90   $1,373.90