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 $169.55   13.509%   $192.4545   $192.45   $192.45   $192.50  
  Purchase #2 $105.39   8.549%   $114.3998   $114.40   $114.40   $114.40  
  Purchase #3 $181.35   11.178%   $201.6213   $201.62   $201.60   $201.60  
  Purchase #4 $84.81   13.750%   $96.4714   $96.47   $96.45   $96.50  
  Purchase #5 $50.68   11.158%   $56.3349   $56.33   $56.35   $56.30  
  Purchase #6 $205.25   13.423%   $232.8007   $232.80   $232.80   $232.80  
  Purchase #7 $56.75   8.535%   $61.5936   $61.59   $61.60   $61.60  
  7 purchase totals = $853.78       $955.6762   $955.66   $955.65   $955.70