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 $49.73   12.392%   $55.8925   $55.89   $55.90   $55.90  
  Purchase #2 $214.87   11.161%   $238.8516   $238.85   $238.85   $238.90  
  Purchase #3 $64.53   11.147%   $71.7232   $71.72   $71.70   $71.70  
  Purchase #4 $44.63   3.504%   $46.1938   $46.19   $46.20   $46.20  
  Purchase #5 $70.35   8.644%   $76.4311   $76.43   $76.45   $76.40  
  Purchase #6 $113.55   9.555%   $124.3997   $124.40   $124.40   $124.40  
  Purchase #7 $163.28   13.318%   $185.0256   $185.03   $185.05   $185.00  
  7 purchase totals = $720.94       $798.5175   $798.51   $798.55   $798.50