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 $228.99   10.516%   $253.0706   $253.07   $253.05   $253.10  
  Purchase #2 $60.76   3.599%   $62.9468   $62.95   $62.95   $62.90  
  Purchase #3 $68.75   4.146%   $71.6004   $71.60   $71.60   $71.60  
  Purchase #4 $150.54   6.442%   $160.2378   $160.24   $160.25   $160.20  
  Purchase #5 $114.75   13.338%   $130.0554   $130.06   $130.05   $130.10  
  Purchase #6 $15.49   6.331%   $16.4707   $16.47   $16.45   $16.50  
  Purchase #7 $212.78   10.670%   $235.4836   $235.48   $235.50   $235.50  
  7 purchase totals = $852.06       $929.8653   $929.87   $929.85   $929.90