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 $239.78   6.768%   $256.0083   $256.01   $256.00   $256.00  
  Purchase #2 $198.71   8.511%   $215.6222   $215.62   $215.60   $215.60  
  Purchase #3 $24.66   6.387%   $26.235   $26.24   $26.25   $26.20  
  Purchase #4 $188.80   13.414%   $214.1256   $214.13   $214.15   $214.10  
  Purchase #5 $220.51   7.542%   $237.1409   $237.14   $237.15   $237.10  
  Purchase #6 $85.67   12.430%   $96.3188   $96.32   $96.30   $96.30  
  Purchase #7 $65.94   10.744%   $73.0246   $73.02   $73.00   $73.00  
  7 purchase totals = $1,024.07       $1,118.4754   $1,118.48   $1,118.45   $1,118.30