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 $118.64   13.493%   $134.6481   $134.65   $134.65   $134.60  
  Purchase #2 $177.42   8.203%   $191.9738   $191.97   $191.95   $192.00  
  Purchase #3 $44.42   9.440%   $48.6132   $48.61   $48.60   $48.60  
  Purchase #4 $138.45   7.553%   $148.9071   $148.91   $148.90   $148.90  
  Purchase #5 $66.76   12.330%   $74.9915   $74.99   $75.00   $75.00  
  Purchase #6 $224.60   6.586%   $239.3922   $239.39   $239.40   $239.40  
  Purchase #7 $166.54   13.723%   $189.3943   $189.39   $189.40   $189.40  
  7 purchase totals = $936.83       $1,027.9202   $1,027.91   $1,027.90   $1,027.90