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 $87.38   12.823%   $98.5847   $98.58   $98.60   $98.60  
  Purchase #2 $125.34   8.866%   $136.4526   $136.45   $136.45   $136.50  
  Purchase #3 $171.58   7.789%   $184.9444   $184.94   $184.95   $184.90  
  Purchase #4 $70.66   8.503%   $76.6682   $76.67   $76.65   $76.70  
  Purchase #5 $164.59   3.231%   $169.9079   $169.91   $169.90   $169.90  
  Purchase #6 $109.43   13.324%   $124.0105   $124.01   $124.00   $124.00  
  Purchase #7 $40.97   13.334%   $46.4329   $46.43   $46.45   $46.40  
  7 purchase totals = $769.95       $837.0012   $836.99   $837.00   $837.00