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 $194.68   13.264%   $220.5024   $220.50   $220.50   $220.50  
  Purchase #2 $115.50   3.832%   $119.926   $119.93   $119.95   $119.90  
  Purchase #3 $72.34   12.602%   $81.4563   $81.46   $81.45   $81.50  
  Purchase #4 $206.61   3.116%   $213.048   $213.05   $213.05   $213.00  
  Purchase #5 $132.25   13.233%   $149.7506   $149.75   $149.75   $149.80  
  Purchase #6 $193.73   11.402%   $215.8191   $215.82   $215.80   $215.80  
  Purchase #7 $248.61   3.778%   $258.0025   $258.00   $258.00   $258.00  
  7 purchase totals = $1,163.72       $1,258.5049   $1,258.51   $1,258.50   $1,258.50