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 $34.34   6.604%   $36.6078   $36.61   $36.60   $36.60  
  Purchase #2 $65.96   5.337%   $69.4803   $69.48   $69.50   $69.50  
  Purchase #3 $183.81   13.744%   $209.0728   $209.07   $209.05   $209.10  
  Purchase #4 $194.92   8.815%   $212.1022   $212.10   $212.10   $212.10  
  Purchase #5 $13.94   13.564%   $15.8308   $15.83   $15.85   $15.80  
  Purchase #6 $240.71   8.693%   $261.6349   $261.63   $261.65   $261.60  
  Purchase #7 $244.94   7.682%   $263.7563   $263.76   $263.75   $263.80  
  7 purchase totals = $978.62       $1,068.4851   $1,068.48   $1,068.50   $1,068.50