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 $62.59   5.745%   $66.1858   $66.19   $66.20   $66.20  
  Purchase #2 $92.38   4.424%   $96.4669   $96.47   $96.45   $96.50  
  Purchase #3 $56.49   3.236%   $58.318   $58.32   $58.30   $58.30  
  Purchase #4 $175.81   7.238%   $188.5351   $188.54   $188.55   $188.50  
  Purchase #5 $214.42   7.395%   $230.2764   $230.28   $230.30   $230.30  
  Purchase #6 $39.33   11.153%   $43.7165   $43.72   $43.70   $43.70  
  Purchase #7 $20.83   12.670%   $23.4692   $23.47   $23.45   $23.50  
  7 purchase totals = $661.85       $706.9679   $706.99   $706.95   $707.00