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 $208.41   3.136%   $214.9457   $214.95   $214.95   $214.90  
  Purchase #2 $122.25   11.422%   $136.2134   $136.21   $136.20   $136.20  
  Purchase #3 $41.27   7.222%   $44.2505   $44.25   $44.25   $44.30  
  Purchase #4 $48.90   7.844%   $52.7357   $52.74   $52.75   $52.70  
  Purchase #5 $129.34   9.825%   $142.0477   $142.05   $142.05   $142.00  
  Purchase #6 $213.33   13.705%   $242.5669   $242.57   $242.55   $242.60  
  Purchase #7 $224.31   10.801%   $248.5377   $248.54   $248.55   $248.50  
  7 purchase totals = $987.81       $1,081.2976   $1,081.31   $1,081.30   $1,081.20