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 $162.57   3.510%   $168.2762   $168.28   $168.30   $168.30  
  Purchase #2 $124.33   6.381%   $132.2635   $132.26   $132.25   $132.30  
  Purchase #3 $55.64   5.478%   $58.688   $58.69   $58.70   $58.70  
  Purchase #4 $240.94   12.644%   $271.4045   $271.40   $271.40   $271.40  
  Purchase #5 $86.50   11.296%   $96.271   $96.27   $96.25   $96.30  
  Purchase #6 $155.25   3.838%   $161.2085   $161.21   $161.20   $161.20  
  Purchase #7 $114.31   11.583%   $127.5505   $127.55   $127.55   $127.60  
  7 purchase totals = $939.54       $1,015.6622   $1,015.66   $1,015.65   $1,015.80