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 $219.51   13.439%   $249.0099   $249.01   $249.00   $249.00  
  Purchase #2 $208.86   12.680%   $235.3434   $235.34   $235.35   $235.30  
  Purchase #3 $117.55   8.543%   $127.5923   $127.59   $127.60   $127.60  
  Purchase #4 $197.41   8.615%   $214.4169   $214.42   $214.40   $214.40  
  Purchase #5 $241.87   13.147%   $273.6686   $273.67   $273.65   $273.70  
  Purchase #6 $79.51   5.661%   $84.0111   $84.01   $84.00   $84.00  
  Purchase #7 $40.43   10.421%   $44.6432   $44.64   $44.65   $44.60  
  7 purchase totals = $1,105.14       $1,228.6854   $1,228.68   $1,228.65   $1,228.60