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 $238.87   9.732%   $262.1168   $262.12   $262.10   $262.10  
  Purchase #2 $46.66   13.615%   $53.0128   $53.01   $53.00   $53.00  
  Purchase #3 $237.76   11.558%   $265.2403   $265.24   $265.25   $265.20  
  Purchase #4 $23.99   8.414%   $26.0085   $26.01   $26.00   $26.00  
  Purchase #5 $213.81   11.554%   $238.5136   $238.51   $238.50   $238.50  
  Purchase #6 $154.80   8.708%   $168.28   $168.28   $168.30   $168.30  
  Purchase #7 $35.29   7.589%   $37.9682   $37.97   $37.95   $38.00  
  7 purchase totals = $951.18       $1,051.1402   $1,051.14   $1,051.10   $1,051.10