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 $183.67   11.749%   $205.2494   $205.25   $205.25   $205.20  
  Purchase #2 $35.47   8.234%   $38.3906   $38.39   $38.40   $38.40  
  Purchase #3 $52.94   7.668%   $56.9994   $57.00   $57.00   $57.00  
  Purchase #4 $121.59   10.603%   $134.4822   $134.48   $134.50   $134.50  
  Purchase #5 $220.55   13.635%   $250.622   $250.62   $250.60   $250.60  
  Purchase #6 $94.29   8.124%   $101.9501   $101.95   $101.95   $102.00  
  Purchase #7 $188.55   9.269%   $206.0267   $206.03   $206.05   $206.00  
  7 purchase totals = $897.06       $993.7204   $993.72   $993.75   $993.70