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 $53.99   7.379%   $57.9739   $57.97   $57.95   $58.00  
  Purchase #2 $139.54   5.678%   $147.4631   $147.46   $147.45   $147.50  
  Purchase #3 $157.33   11.860%   $175.9893   $175.99   $176.00   $176.00  
  Purchase #4 $121.38   10.852%   $134.5522   $134.55   $134.55   $134.60  
  Purchase #5 $23.47   9.747%   $25.7576   $25.76   $25.75   $25.80  
  Purchase #6 $235.63   11.610%   $262.9866   $262.99   $263.00   $263.00  
  Purchase #7 $177.63   6.125%   $188.5098   $188.51   $188.50   $188.50  
  7 purchase totals = $908.97       $993.2325   $993.23   $993.20   $993.40