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 $249.55   12.604%   $281.0033   $281.00   $281.00   $281.00  
  Purchase #2 $222.45   3.854%   $231.0232   $231.02   $231.00   $231.00  
  Purchase #3 $162.53   13.290%   $184.1302   $184.13   $184.15   $184.10  
  Purchase #4 $181.32   6.770%   $193.5954   $193.60   $193.60   $193.60  
  Purchase #5 $56.93   12.570%   $64.0861   $64.09   $64.10   $64.10  
  Purchase #6 $69.29   10.477%   $76.5495   $76.55   $76.55   $76.50  
  Purchase #7 $33.36   4.490%   $34.8579   $34.86   $34.85   $34.90  
  7 purchase totals = $975.43       $1,065.2456   $1,065.25   $1,065.25   $1,065.20