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 $65.88   3.591%   $68.2458   $68.25   $68.25   $68.20  
  Purchase #2 $224.87   7.602%   $241.9646   $241.96   $241.95   $242.00  
  Purchase #3 $45.78   5.439%   $48.27   $48.27   $48.25   $48.30  
  Purchase #4 $170.49   11.806%   $190.618   $190.62   $190.60   $190.60  
  Purchase #5 $175.34   4.309%   $182.8954   $182.90   $182.90   $182.90  
  Purchase #6 $185.81   9.632%   $203.7072   $203.71   $203.70   $203.70  
  Purchase #7 $28.35   4.224%   $29.5475   $29.55   $29.55   $29.50  
  7 purchase totals = $896.52       $965.2485   $965.26   $965.20   $965.20