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 $218.39   11.687%   $243.9132   $243.91   $243.90   $243.90  
  Purchase #2 $103.62   4.198%   $107.97   $107.97   $107.95   $108.00  
  Purchase #3 $44.57   4.866%   $46.7388   $46.74   $46.75   $46.70  
  Purchase #4 $174.91   6.696%   $186.622   $186.62   $186.60   $186.60  
  Purchase #5 $241.66   3.353%   $249.7629   $249.76   $249.75   $249.80  
  Purchase #6 $28.93   12.156%   $32.4467   $32.45   $32.45   $32.40  
  Purchase #7 $212.84   13.802%   $242.2162   $242.22   $242.20   $242.20  
  7 purchase totals = $1,024.92       $1,109.6698   $1,109.67   $1,109.60   $1,109.60