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 $53.86   8.484%   $58.4295   $58.43   $58.45   $58.40  
  Purchase #2 $86.77   5.636%   $91.6604   $91.66   $91.65   $91.70  
  Purchase #3 $14.72   12.231%   $16.5204   $16.52   $16.50   $16.50  
  Purchase #4 $115.83   3.161%   $119.4914   $119.49   $119.50   $119.50  
  Purchase #5 $46.34   5.172%   $48.7367   $48.74   $48.75   $48.70  
  Purchase #6 $219.62   6.855%   $234.675   $234.68   $234.70   $234.70  
  Purchase #7 $8.25   3.618%   $8.5485   $8.55   $8.55   $8.50  
  7 purchase totals = $545.39       $578.0619   $578.07   $578.10   $578.00