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 $62.95   10.615%   $69.6321   $69.63   $69.65   $69.60  
  Purchase #2 $20.69   9.513%   $22.6582   $22.66   $22.65   $22.70  
  Purchase #3 $122.75   6.523%   $130.757   $130.76   $130.75   $130.80  
  Purchase #4 $191.96   8.531%   $208.3361   $208.34   $208.35   $208.30  
  Purchase #5 $202.60   11.836%   $226.5797   $226.58   $226.60   $226.60  
  Purchase #6 $146.37   8.581%   $158.93   $158.93   $158.95   $158.90  
  Purchase #7 $29.88   9.430%   $32.6977   $32.70   $32.70   $32.70  
  7 purchase totals = $777.20       $849.5908   $849.60   $849.65   $849.60