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 $226.97   5.282%   $238.9586   $238.96   $238.95   $239.00  
  Purchase #2 $246.50   8.126%   $266.5306   $266.53   $266.55   $266.50  
  Purchase #3 $81.62   3.539%   $84.5085   $84.51   $84.50   $84.50  
  Purchase #4 $32.38   10.759%   $35.8638   $35.86   $35.85   $35.90  
  Purchase #5 $42.58   13.842%   $48.4739   $48.47   $48.45   $48.50  
  Purchase #6 $192.95   11.160%   $214.4832   $214.48   $214.50   $214.50  
  Purchase #7 $73.83   13.506%   $83.8015   $83.80   $83.80   $83.80  
  7 purchase totals = $896.83       $972.6201   $972.61   $972.60   $972.70