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 $8.89   11.680%   $9.9284   $9.93   $9.95   $9.90  
  Purchase #2 $73.88   12.718%   $83.2761   $83.28   $83.30   $83.30  
  Purchase #3 $130.59   5.263%   $137.463   $137.46   $137.45   $137.50  
  Purchase #4 $200.97   6.641%   $214.3164   $214.32   $214.30   $214.30  
  Purchase #5 $214.66   4.376%   $224.0535   $224.05   $224.05   $224.10  
  Purchase #6 $116.27   3.715%   $120.5894   $120.59   $120.60   $120.60  
  Purchase #7 $120.73   8.395%   $130.8653   $130.87   $130.85   $130.90  
  7 purchase totals = $865.99       $920.4921   $920.50   $920.50   $920.60