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 $86.81   11.676%   $96.9459   $96.95   $96.95   $96.90  
  Purchase #2 $248.86   12.567%   $280.1342   $280.13   $280.15   $280.10  
  Purchase #3 $200.63   5.655%   $211.9756   $211.98   $212.00   $212.00  
  Purchase #4 $157.43   11.669%   $175.8005   $175.80   $175.80   $175.80  
  Purchase #5 $108.73   6.153%   $115.4202   $115.42   $115.40   $115.40  
  Purchase #6 $141.70   10.379%   $156.407   $156.41   $156.40   $156.40  
  Purchase #7 $52.80   4.242%   $55.0398   $55.04   $55.05   $55.00  
  7 purchase totals = $996.96       $1,091.7232   $1,091.73   $1,091.75   $1,091.60