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 $172.42   13.380%   $195.4898   $195.49   $195.50   $195.50  
  Purchase #2 $128.95   11.558%   $143.854   $143.85   $143.85   $143.90  
  Purchase #3 $21.46   11.251%   $23.8745   $23.87   $23.85   $23.90  
  Purchase #4 $62.86   10.446%   $69.4264   $69.43   $69.45   $69.40  
  Purchase #5 $86.38   13.807%   $98.3065   $98.31   $98.30   $98.30  
  Purchase #6 $63.97   6.322%   $68.0142   $68.01   $68.00   $68.00  
  Purchase #7 $159.38   11.207%   $177.2417   $177.24   $177.25   $177.20  
  7 purchase totals = $695.42       $776.2071   $776.20   $776.20   $776.20