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 $147.41   10.208%   $162.4576   $162.46   $162.45   $162.50  
  Purchase #2 $59.39   8.464%   $64.4168   $64.42   $64.40   $64.40  
  Purchase #3 $5.49   8.241%   $5.9424   $5.94   $5.95   $5.90  
  Purchase #4 $234.81   11.821%   $262.5669   $262.57   $262.55   $262.60  
  Purchase #5 $63.55   11.225%   $70.6835   $70.68   $70.70   $70.70  
  Purchase #6 $22.76   9.543%   $24.932   $24.93   $24.95   $24.90  
  Purchase #7 $237.66   6.803%   $253.828   $253.83   $253.85   $253.80  
  7 purchase totals = $771.07       $844.8272   $844.83   $844.85   $844.80