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 $66.98   9.260%   $73.1823   $73.18   $73.20   $73.20  
  Purchase #2 $53.38   6.275%   $56.7296   $56.73   $56.75   $56.70  
  Purchase #3 $66.99   12.215%   $75.1728   $75.17   $75.15   $75.20  
  Purchase #4 $58.47   13.349%   $66.2752   $66.28   $66.30   $66.30  
  Purchase #5 $82.49   4.856%   $86.4957   $86.50   $86.50   $86.50  
  Purchase #6 $119.62   13.432%   $135.6874   $135.69   $135.70   $135.70  
  Purchase #7 $58.81   12.228%   $66.0013   $66.00   $66.00   $66.00  
  7 purchase totals = $506.74       $559.5443   $559.55   $559.60   $559.60