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 $85.45   8.329%   $92.5671   $92.57   $92.55   $92.60  
  Purchase #2 $186.87   7.520%   $200.9226   $200.92   $200.90   $200.90  
  Purchase #3 $245.88   9.776%   $269.9172   $269.92   $269.90   $269.90  
  Purchase #4 $246.89   5.849%   $261.3306   $261.33   $261.35   $261.30  
  Purchase #5 $88.82   4.445%   $92.768   $92.77   $92.75   $92.80  
  Purchase #6 $32.60   12.368%   $36.632   $36.63   $36.65   $36.60  
  Purchase #7 $21.84   7.482%   $23.4741   $23.47   $23.45   $23.50  
  7 purchase totals = $908.35       $977.6116   $977.61   $977.55   $977.60