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 $60.69   3.259%   $62.6679   $62.67   $62.65   $62.70  
  Purchase #2 $129.69   10.796%   $143.6913   $143.69   $143.70   $143.70  
  Purchase #3 $72.33   3.485%   $74.8507   $74.85   $74.85   $74.90  
  Purchase #4 $144.40   9.443%   $158.0357   $158.04   $158.05   $158.00  
  Purchase #5 $188.60   5.320%   $198.6335   $198.63   $198.65   $198.60  
  Purchase #6 $224.65   10.486%   $248.2068   $248.21   $248.20   $248.20  
  Purchase #7 $78.25   8.510%   $84.9091   $84.91   $84.90   $84.90  
  7 purchase totals = $898.61       $970.9950   $971.00   $971.00   $971.00