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 $218.84   7.484%   $235.218   $235.22   $235.20   $235.20  
  Purchase #2 $41.51   4.185%   $43.2472   $43.25   $43.25   $43.20  
  Purchase #3 $29.32   9.432%   $32.0855   $32.09   $32.10   $32.10  
  Purchase #4 $123.57   9.635%   $135.476   $135.48   $135.50   $135.50  
  Purchase #5 $168.75   5.446%   $177.9401   $177.94   $177.95   $177.90  
  Purchase #6 $182.63   11.641%   $203.89   $203.89   $203.90   $203.90  
  Purchase #7 $15.31   11.165%   $17.0194   $17.02   $17.00   $17.00  
  7 purchase totals = $779.93       $844.8762   $844.89   $844.90   $844.80