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 $230.66   8.187%   $249.5441   $249.54   $249.55   $249.50  
  Purchase #2 $10.71   8.212%   $11.5895   $11.59   $11.60   $11.60  
  Purchase #3 $144.61   11.496%   $161.2344   $161.23   $161.25   $161.20  
  Purchase #4 $119.37   13.391%   $135.3548   $135.35   $135.35   $135.40  
  Purchase #5 $215.54   6.688%   $229.9553   $229.96   $229.95   $230.00  
  Purchase #6 $127.31   8.844%   $138.5693   $138.57   $138.55   $138.60  
  Purchase #7 $175.81   9.719%   $192.897   $192.90   $192.90   $192.90  
  7 purchase totals = $1,024.01       $1,119.1444   $1,119.14   $1,119.15   $1,119.20