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 $63.68   8.874%   $69.331   $69.33   $69.35   $69.30  
  Purchase #2 $122.94   7.162%   $131.745   $131.75   $131.75   $131.70  
  Purchase #3 $185.74   3.345%   $191.953   $191.95   $191.95   $192.00  
  Purchase #4 $230.70   3.280%   $238.267   $238.27   $238.25   $238.30  
  Purchase #5 $20.67   11.473%   $23.0415   $23.04   $23.05   $23.00  
  Purchase #6 $60.83   8.430%   $65.958   $65.96   $65.95   $66.00  
  Purchase #7 $60.66   7.426%   $65.1646   $65.16   $65.15   $65.20  
  7 purchase totals = $745.22       $785.4601   $785.46   $785.45   $785.50