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 $38.36   11.298%   $42.6939   $42.69   $42.70   $42.70  
  Purchase #2 $70.44   8.447%   $76.3901   $76.39   $76.40   $76.40  
  Purchase #3 $202.52   8.119%   $218.9626   $218.96   $218.95   $219.00  
  Purchase #4 $47.75   8.827%   $51.9649   $51.96   $51.95   $52.00  
  Purchase #5 $193.86   10.423%   $214.066   $214.07   $214.05   $214.10  
  Purchase #6 $207.32   4.147%   $215.9176   $215.92   $215.90   $215.90  
  Purchase #7 $13.39   6.606%   $14.2745   $14.27   $14.25   $14.30  
  7 purchase totals = $773.64       $834.2696   $834.26   $834.20   $834.40