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 $59.30   3.252%   $61.2284   $61.23   $61.25   $61.20  
  Purchase #2 $114.29   12.564%   $128.6494   $128.65   $128.65   $128.60  
  Purchase #3 $30.51   6.849%   $32.5996   $32.60   $32.60   $32.60  
  Purchase #4 $186.36   6.612%   $198.6821   $198.68   $198.70   $198.70  
  Purchase #5 $57.56   7.573%   $61.919   $61.92   $61.90   $61.90  
  Purchase #6 $192.72   8.309%   $208.7331   $208.73   $208.75   $208.70  
  Purchase #7 $74.51   13.378%   $84.4779   $84.48   $84.50   $84.50  
  7 purchase totals = $715.25       $776.2895   $776.29   $776.35   $776.20